<h2>Prerequisites</h2>



<p>There are a few things you should know in advance before you start playing around with React.</p>



<p>Here are what I consider to be React prerequisites.</p>



<ul><li>Basic familiarity with HTML &amp; CSS.</li><li>Basic knowledge of JavaScript and programming.</li><li>Basic understanding of the <a rel="noreferrer noopener" aria-label="DOM (opens in a new tab)" href="https://www.w3schools.com/js/js_htmldom.asp" target="_blank">DOM</a>.</li><li>Familiarity with ES6 syntax and features.</li><li><a href="http://ec2-13-127-91-65.ap-south-1.compute.amazonaws.com/how-to-install-and-manage-node-js-via-nvm/">Node.js and npm</a> installed globally.</li></ul>



<h2>Setup and Installation</h2>



<p><strong><em>npx create-react-app</em></strong> is the command to setup and install a react app. Its a built in package comes with nodejs. Run the below command to create a react app. It will take some time, wait for it to complete the setup.</p>



<pre class="wp-block-code"><code>npx create-react-app react-app</code></pre>



<p>Here <strong><em>react-app</em></strong> is the folder name in which react config &amp; setup files will be created by react to run a react-app.</p>



<div class="wp-block-image"><figure class="aligncenter size-large"><img src="http://ec2-13-127-91-65.ap-south-1.compute.amazonaws.com/wp-content/uploads/2020/03/Screenshot-from-2020-03-01-14-19-45-1024x575.png" alt="" class="wp-image-676"/></figure></div>



<div class="wp-block-image"><figure class="aligncenter size-large"><img src="http://ec2-13-127-91-65.ap-south-1.compute.amazonaws.com/wp-content/uploads/2020/03/Screenshot-from-2020-03-01-14-19-55-1024x575.png" alt="" class="wp-image-677"/></figure></div>



<p>Go to newly created app and run the below command to run the app.</p>



<pre class="wp-block-code"><code>cd react-app
npm start</code></pre>



<p><strong><em>npm start</em></strong> will run your react app.</p>



<div class="wp-block-image"><figure class="aligncenter size-large"><img src="http://ec2-13-127-91-65.ap-south-1.compute.amazonaws.com/wp-content/uploads/2020/03/Screenshot-from-2020-03-01-14-22-32-1024x575.png" alt="" class="wp-image-678"/></figure></div>



<p>Now, Edit <strong><em>src/App.js</em></strong> and save to view the effect.</p>



<p>Feel free to leave a comment for any questions and issues.</p>

Prerequisites



There are a few things you should know in advance before you start playing around with React.



Here are what I consider to be ...

Getting Started with React - TCMHACK

Getting Started with React

<p>An important aspect of web components is encapsulation — being able to keep the markup structure, style, and behavior hidden and separate from other code on the page so that different parts do not clash, and the code can be kept nice and clean. The Shadow DOM API is a key part of this, providing a way to attach a hidden separated DOM to an element. This article covers the basics of using the Shadow DOM.</p>



<blockquote class="wp-block-quote"><p><strong>Note</strong>: Shadow DOM is supported by default in Firefox (63 and onwards), Chrome, Opera, and Safari. The new Chromium-based Edge (79 and onwards) supports it too; the old Edge didn't.</p></blockquote>



<h2>High-level view</h2>



<p>This article assumes you are already familiar with the concept of the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Document_Object_Model/Introduction" target="_blank" rel="noreferrer noopener nofollow">DOM (Document Object Model)</a> — a tree-like structure of connected nodes that represents the different elements and strings of text appearing in a markup document (usually an HTML document in the case of web documents). As an example, consider the following HTML fragment:</p>



<pre class="wp-block-code"><code>&lt;!DOCTYPE html&gt;
&lt;html&gt;
  &lt;head&gt;
    &lt;meta charset="utf-8"&gt;
    &lt;title&gt;Simple DOM example&lt;/title&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;section&gt;
        &lt;img src="dinosaur.png" alt="A red Tyrannosaurus Rex: A two legged dinosaur standing upright like a human, with small arms, and a large head with lots of sharp teeth."&gt;
        &lt;p&gt;Here we will add a link to the &lt;a href="https://www.mozilla.org/"&gt;Mozilla homepage&lt;/a&gt;&lt;/p&gt;
      &lt;/section&gt;
  &lt;/body&gt;
&lt;/html&gt;</code></pre>



<p>This fragment produces the following DOM structure:</p>



<figure class="wp-block-image size-full"><img src="https://tcmhack.in/wp-content/uploads/2021/09/dom-screenshot.png" alt="" class="wp-image-869"/></figure>



<p><em>Shadow DOM</em> allows hidden DOM trees to be attached to elements in the regular DOM tree — this shadow DOM tree starts with a shadow root, underneath which can be attached to any elements you want, in the same way as the normal DOM.</p>



<figure class="wp-block-image size-large"><img src="https://tcmhack.in/wp-content/uploads/2021/09/shadowdom-1-1024x471.png" alt="" class="wp-image-870"/></figure>



<p>There are some bits of shadow DOM terminology to be aware of:</p>



<ul><li><strong>Shadow host:</strong> The regular DOM node that the shadow DOM is attached to.</li><li><strong>Shadow tree:</strong> The DOM tree inside the shadow DOM.</li><li><strong>Shadow boundary:</strong> the place where the shadow DOM ends, and the regular DOM begins.</li><li><strong>Shadow root:</strong> The root node of the shadow tree.</li></ul>



<p>You can affect the nodes in the shadow DOM in exactly the same way as non-shadow nodes — for example appending children or setting attributes, styling individual nodes using element.style.foo, or adding style to the entire shadow DOM tree inside a<a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/style" target="_blank" rel="noreferrer noopener nofollow"> <code>&lt;style&gt;</code></a> element. The difference is that none of the code inside a shadow DOM can affect anything outside it, allowing for handy encapsulation.</p>



<p>Note that the shadow DOM is not a new thing by any means — browsers have used it for a long time to encapsulate the inner structure of an element. Think for example of a <code><a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/video" target="_blank" rel="noreferrer noopener nofollow">&lt;video&gt;</a></code> element, with the default browser controls exposed. All you see in the DOM is the <code>&lt;video&gt;</code> element, but it contains a series of buttons and other controls inside its shadow DOM. The shadow DOM spec has made it so that you are allowed to actually manipulate the shadow DOM of your own custom elements.</p>



<h2>Basic usage</h2>



<p>You can attach a shadow root to any element using the&nbsp;<a href="https://developer.mozilla.org/en-US/docs/Web/API/Element/attachShadow" target="_blank" rel="noreferrer noopener nofollow"><code>Element.attachShadow()</code></a>&nbsp;method. This takes as its parameter an options object that contains one option —&nbsp;<code>mode</code>&nbsp;— with a value of&nbsp;<code>open</code>&nbsp;or&nbsp;<code>closed</code>:</p>



<pre class="wp-block-code"><code>let shadow = elementRef.attachShadow({mode: 'open'});
let shadow = elementRef.attachShadow({mode: 'closed'});</code></pre>



<p><code>open</code>&nbsp;means that you can access the shadow DOM using JavaScript written in the main page context, for example using the&nbsp;<a href="https://developer.mozilla.org/en-US/docs/Web/API/Element/shadowRoot" target="_blank" rel="noreferrer noopener nofollow"><code>Element.shadowRoot</code></a>&nbsp;property:</p>



<pre class="wp-block-code"><code>let myShadowDom = myCustomElem.shadowRoot;</code></pre>



<p>If you attach a shadow root to a custom element with&nbsp;<code>mode: closed</code>&nbsp;set, you won't be able to access the shadow DOM from the outside —&nbsp;<code>myCustomElem.shadowRoot</code>&nbsp;returns&nbsp;<code>null</code>. This is the case with built in elements that contain shadow DOMs, such as&nbsp;<code>&lt;video&gt;</code>.</p>



<p><strong>Note</strong>: As&nbsp;<a href="https://blog.revillweb.com/open-vs-closed-shadow-dom-9f3d7427d1af" target="_blank" rel="noreferrer noopener nofollow">this blog post shows</a>, it is actually fairly easy to work around closed shadow DOMs, and the hassle to completely hide them is often more than it's worth.</p>



<p>If you are attaching a shadow DOM to a custom element as part of its constructor (by far the most useful application of the shadow DOM), you would use something like this:</p>



<pre class="wp-block-code"><code>let shadow = this.attachShadow({mode: 'open'});</code></pre>



<p>When you've attached a shadow DOM to an element, manipulating it is a matter of just using the same DOM APIs as you use for the regular DOM manipulation:</p>



<pre class="wp-block-code"><code>let para = document.createElement('p');
shadow.appendChild(para);
// etc.</code></pre>



<h2 id="working_through_a_simple_example">Working through a simple example</h2>



<p>Now let's walk through a simple example to demonstrate the shadow DOM in action inside a custom element —&nbsp;<code><a href="https://github.com/mdn/web-components-examples/tree/master/popup-info-box-web-component" target="_blank" rel="noreferrer noopener nofollow">&lt;popup-info&gt;</a></code>&nbsp;(see a&nbsp;<a href="https://mdn.github.io/web-components-examples/popup-info-box-web-component/" target="_blank" rel="noreferrer noopener nofollow">live example</a>&nbsp;also). This takes an image icon and a text string, and embeds the icon into the page. When the icon is focused, it displays the text in a pop up information box to provide further in-context information. To begin with, in our JavaScript file we define a class called&nbsp;<code>PopUpInfo</code>, which extends&nbsp;<code>HTMLElement</code>:</p>



<pre class="wp-block-code"><code>class PopUpInfo extends HTMLElement {
  constructor() {
    // Always call super first in constructor
    super();

    // write element functionality in here

    ...
  }
}</code></pre>



<p>Inside the class definition we define the element's constructor, which defines all the functionality the element will have when an instance of it is instantiated.</p>



<h3 id="creating_the_shadow_root">Creating the shadow root</h3>



<p>We first attach a shadow root to the custom element:</p>



<pre class="wp-block-code"><code>// Create a shadow root
let shadow = this.attachShadow({mode: 'open'});</code></pre>



<h3 id="creating_the_shadow_dom_structure">Creating the shadow DOM structure</h3>



<p>Next, we use some DOM manipulation to create the element's internal shadow DOM structure:</p>



<pre class="wp-block-code"><code>// Create spans
let wrapper = document.createElement('span');
wrapper.setAttribute('class', 'wrapper');
let icon = document.createElement('span');
icon.setAttribute('class', 'icon');
icon.setAttribute('tabindex', 0);
let info = document.createElement('span');
info.setAttribute('class', 'info');

// Take attribute content and put it inside the info span
let text = this.getAttribute('data-text');
info.textContent = text;

// Insert icon
let imgUrl;
if(this.hasAttribute('img')) {
  imgUrl = this.getAttribute('img');
} else {
  imgUrl = 'img/default.png';
}
let img = document.createElement('img');
img.src = imgUrl;
icon.appendChild(img);
</code></pre>



<h3 id="styling_the_shadow_dom">Styling the shadow DOM</h3>



<p>After that we create a&nbsp;<a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/style" target="_blank" rel="noreferrer noopener nofollow"><code>&lt;style&gt;</code></a>&nbsp;element and populate it with some CSS to style it:</p>



<pre class="wp-block-code"><code>// Create some CSS to apply to the shadow dom
let style = document.createElement('style');

style.textContent = `
.wrapper {
  position: relative;
}

.info {
  font-size: 0.8rem;
  width: 200px;
  display: inline-block;
  border: 1px solid black;
  padding: 10px;
  background: white;
  border-radius: 10px;
  opacity: 0;
  transition: 0.6s all;
  position: absolute;
  bottom: 20px;
  left: 10px;
  z-index: 3;
}

img {
  width: 1.2rem;
}

.icon:hover + .info, .icon:focus + .info {
  opacity: 1;
}`;</code></pre>



<h3 id="attaching_the_shadow_dom_to_the_shadow_root">Attaching the shadow DOM to the shadow root</h3>



<p>The final step is to attach all the created elements to the shadow root:</p>



<pre class="wp-block-code"><code>// attach the created elements to the shadow dom
shadow.appendChild(style);
shadow.appendChild(wrapper);
wrapper.appendChild(icon);
wrapper.appendChild(info);</code></pre>



<p>Feel free to ask a question in comments.</p>

An important aspect of web components is encapsulation — being able to keep the markup structure, style, and behavior hidden and separate from ot...

Shadow DOM in JavaScript - TCMHACK

Shadow DOM in JavaScript

<h1>Set</h1><p>The&nbsp;<code><strong>Set</strong></code>&nbsp;object lets you store unique values of any type, whether&nbsp;<a href="https://developer.mozilla.org/en-US/docs/Glossary/Primitive" rel="noopener noreferrer" target="_blank">primitive values</a>&nbsp;or object references.</p><h2>Description</h2><p><code>Set</code>&nbsp;objects are collections of values. You can iterate through the elements of a set in insertion order. A value in the&nbsp;<code>Set</code>&nbsp;<strong>may only occur once</strong>; it is unique in the&nbsp;<code>Set</code>'s collection.</p><h3>Value Equality</h3><p>Because each value in the&nbsp;<code>Set</code>&nbsp;has to be unique, the value equality will be checked. In an earlier version of ECMAScript specification, this was not based on the same algorithm as the one used in the&nbsp;<code>===</code>&nbsp;operator. Specifically, for&nbsp;<code>Set</code>s,&nbsp;<code>+0</code>&nbsp;(which is strictly equal to&nbsp;<code>-0</code>) and&nbsp;<code>-0</code>&nbsp;were different values. However, this was changed in the ECMAScript 2015 specification. See&nbsp;<em>"Key equality for -0 and 0"</em>&nbsp;in the&nbsp;browser compatibility&nbsp;table for details.</p><p><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN" rel="noopener noreferrer" target="_blank">NaN</a></code>&nbsp;and&nbsp;<code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined" rel="noopener noreferrer" target="_blank">undefined</a></code>&nbsp;can also be stored in a Set. All&nbsp;<code>NaN</code>&nbsp;values are equated (i.e.&nbsp;<code>NaN</code>&nbsp;is considered the same as&nbsp;<code>NaN</code>, even though&nbsp;<code>NaN !== NaN</code>).</p><h2>Constructor</h2><p><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/Set" rel="noopener noreferrer" target="_blank">Set()</a></code> Creates a new&nbsp;<code>Set</code>&nbsp;object.</p><h2>Static properties</h2><p><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/@@species" rel="noopener noreferrer" target="_blank">get Set[@@species]</a></code> The constructor function that is used to create derived objects.</p><h2>Instance properties</h2><p><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/size" rel="noopener noreferrer" target="_blank">Set.prototype.size</a></code> Returns the number of values in the&nbsp;<code>Set</code>&nbsp;object.</p><h2>Instance methods</h2><ol><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/add" rel="noopener noreferrer" target="_blank">Set.prototype.add(value)</a></code> Appends&nbsp;<code>value</code>&nbsp;to the&nbsp;<code>Set</code>&nbsp;object. Returns the&nbsp;<code>Set</code>&nbsp;object with added value.</li><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/clear" rel="noopener noreferrer" target="_blank">Set.prototype.clear()</a></code> Removes all elements from the&nbsp;<code>Set</code>&nbsp;object.</li><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/delete" rel="noopener noreferrer" target="_blank">Set.prototype.delete(value)</a></code> Removes the element associated to the&nbsp;<code>value</code>&nbsp;and returns a boolean asserting whether an element was successfully removed or not.&nbsp;<code>Set.prototype.has(value)</code>&nbsp;will return&nbsp;<code>false</code>&nbsp;afterwards.</li><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/has" rel="noopener noreferrer" target="_blank">Set.prototype.has(value)</a></code> Returns a boolean asserting whether an element is present with the given value in the&nbsp;<code>Set</code>&nbsp;object or not.</li></ol><h3>Iteration methods</h3><ol><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/@@iterator" rel="noopener noreferrer" target="_blank">Set.prototype[@@iterator]()</a></code> Returns a new iterator object that yields the&nbsp;<strong>values</strong>&nbsp;for each element in the&nbsp;<code>Set</code>&nbsp;object in insertion order.</li><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/values" rel="noopener noreferrer" target="_blank">Set.prototype.keys()</a></code> Returns a new iterator object that yields the values for each element in the&nbsp;<code>Set</code>&nbsp;object in insertion order. (For Sets, this is the same as the&nbsp;<code><strong>values()</strong></code>&nbsp;method.)</li><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/values" rel="noopener noreferrer" target="_blank">Set.prototype.values()</a></code> Returns a new iterator object that yields the&nbsp;<strong>values</strong>&nbsp;for each element in the&nbsp;<code>Set</code>&nbsp;object in insertion order. (For Sets, this is the same as the&nbsp;<code><strong>keys()</strong></code>&nbsp;method.)</li><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/entries" rel="noopener noreferrer" target="_blank">Set.prototype.entries()</a></code> Returns a new iterator object that contains&nbsp;<strong>an array of&nbsp;</strong><code><strong>[value,&nbsp;value]</strong></code>&nbsp;for each element in the&nbsp;<code>Set</code>&nbsp;object, in insertion order. This is similar to the&nbsp;<code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" rel="noopener noreferrer" target="_blank">Map</a></code>&nbsp;object, so that each entry's&nbsp;<em>key</em>&nbsp;is the same as its&nbsp;<em>value</em>&nbsp;for a&nbsp;<code>Set</code>.</li><li><code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/forEach" rel="noopener noreferrer" target="_blank">Set.prototype.forEach(callbackFn[,&nbsp;thisArg])</a></code> Calls&nbsp;<code>callbackFn</code>&nbsp;once for each value present in the&nbsp;<code>Set</code>&nbsp;object, in insertion order. If a&nbsp;<code>thisArg</code>&nbsp;parameter is provided, it will be used as the&nbsp;<code>this</code>&nbsp;value for each invocation of&nbsp;<code>callbackFn</code>.</li></ol><h2>Examples</h2><h3>Using the Set object</h3><pre class="ql-syntax" spellcheck="false">const mySet1 = new Set()

mySet1.add(1)           // Set [ 1 ]
mySet1.add(5)           // Set [ 1, 5 ]
mySet1.add(5)           // Set [ 1, 5 ]
mySet1.add('some text') // Set [ 1, 5, 'some text' ]
const o = {a: 1, b: 2}
mySet1.add(o)

mySet1.add({a: 1, b: 2})   // o is referencing a different object, so this is okay
mySet1.has(1)              // true
mySet1.has(3)              // false, since 3 has not been added to the set
mySet1.has(5)              // true
mySet1.has(Math.sqrt(25))  // true
mySet1.has('Some Text'.toLowerCase()) // true
mySet1.has(o)       // true

mySet1.size         // 5

mySet1.delete(5)    // removes 5 from the set
mySet1.has(5)       // false, 5 has been removed

mySet1.size         // 4, since we just removed one value

console.log(mySet1)
// logs Set(4) [ 1, "some text", {…}, {…} ] in Firefox
// logs Set(4) { 1, "some text", {…}, {…} } in Chrome
</pre><h3>Iterating Sets</h3><pre class="ql-syntax" spellcheck="false">// iterate over items in set
// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1) console.log(item)

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1.keys()) console.log(item)

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
for (let item of mySet1.values()) console.log(item)

// logs the items in the order: 1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}
// (key and value are the same here)
for (let [key, value] of mySet1.entries()) console.log(key)

// convert Set object to an Array object, with Array.from
const myArr = Array.from(mySet1) // [1, "some text", {"a": 1, "b": 2}, {"a": 1, "b": 2}]

// the following will also work if run in an HTML document
mySet1.add(document.body)
mySet1.has(document.querySelector('body')) // true

// converting between Set and Array
const mySet2 = new Set([1, 2, 3, 4])
mySet2.size                    // 4
[...mySet2]                    // [1, 2, 3, 4]

// intersect can be simulated via
const intersection = new Set([...mySet1].filter(x =&gt; mySet2.has(x)))

// difference can be simulated via
const difference = new Set([...mySet1].filter(x =&gt; !mySet2.has(x)))

// Iterate set entries with forEach()
mySet1.forEach(function(value) {
  console.log(value)
})

// 1
// 2
// 3
// 4
</pre><h3>Implementing basic set operations</h3><pre class="ql-syntax" spellcheck="false">function isSuperset(set, subset) {
    for (let elem of subset) {
        if (!set.has(elem)) {
            return false
        }
    }
    return true
}

function union(setA, setB) {
    let _union = new Set(setA)
    for (let elem of setB) {
        _union.add(elem)
    }
    return _union
}

function intersection(setA, setB) {
    let _intersection = new Set()
    for (let elem of setB) {
        if (setA.has(elem)) {
            _intersection.add(elem)
        }
    }
    return _intersection
}

function symmetricDifference(setA, setB) {
    let _difference = new Set(setA)
    for (let elem of setB) {
        if (_difference.has(elem)) {
            _difference.delete(elem)
        } else {
            _difference.add(elem)
        }
    }
    return _difference
}

function difference(setA, setB) {
    let _difference = new Set(setA)
    for (let elem of setB) {
        _difference.delete(elem)
    }
    return _difference
}

// Examples
const setA = new Set([1, 2, 3, 4])
const setB = new Set([2, 3])
const setC = new Set([3, 4, 5, 6])

isSuperset(setA, setB)          // returns true
union(setA, setC)               // returns Set {1, 2, 3, 4, 5, 6}
intersection(setA, setC)        // returns Set {3, 4}
symmetricDifference(setA, setC) // returns Set {1, 2, 5, 6}
difference(setA, setC)          // returns Set {1, 2}

</pre><h3>Relation with Array objects</h3><pre class="ql-syntax" spellcheck="false">let myArray = ['value1', 'value2', 'value3']

// Use the regular Set constructor to transform an Array into a Set
let mySet = new Set(myArray)

mySet.has('value1')     // returns true

// Use the spread operator to transform a set into an Array.
console.log([...mySet]) // Will show you exactly the same Array as myArray
</pre><h3>Remove duplicate elements from the array</h3><pre class="ql-syntax" spellcheck="false">// Use to remove duplicate elements from the array

const numbers = [2,3,4,4,2,3,3,4,4,5,5,6,6,7,5,32,3,4,5]

console.log([...new Set(numbers)])
// [2, 3, 4, 5, 6, 7, 32]
</pre><h3>Relation with Strings</h3><pre class="ql-syntax" spellcheck="false">let text = 'India'

const mySet = new Set(text)  // Set(5) {'I', 'n', 'd', 'i', 'a'}
mySet.size  // 5

//case sensitive &amp; duplicate ommision
new Set("Firefox")  // Set(7) { "F", "i", "r", "e", "f", "o", "x" }
new Set("firefox")  // Set(6) { "f", "i", "r", "e", "o", "x" }
</pre><h3>Use Set to ensure the uniqueness of a list of values</h3><pre class="ql-syntax" spellcheck="false">const array = Array.from(document.querySelectorAll('[id]')).map(e =&gt; e.id);
const set = new Set(array);
console.assert(set.size == array.length);
</pre><p>That's how Set works in JavaScript. Feel free to leave a comment below.</p>

The Set object lets you store unique values of any type, whether primitive values or object references. Set objects are collections of values. You can iterate through the elements of a set in insertion order. A value in the Set may only occur once; it is unique in the Set's collectionThe Set object lets you store unique values of any type, whether primitive values or object references. Set objects are collections of values...

Explanation & Working of Set's in JavaScript - TCMHACK

Explanation & Working of Set's in JavaScript

<p>React library to support easy Zoom, Pan, Pinch on various html dom elements like Images and Div's. It is a Super fast and light react npm package for Zooming, Panning and Pinching html elements in easy way.</p><h2>Features</h2><ul><li><strong>Fast and easy to use</strong></li><li><strong>Light, without external dependencies</strong></li><li><strong>Mobile gestures, touchpad gestures and desktop mouse events support</strong></li><li><strong>Powerful context usage, which gives you a lot of freedom</strong></li><li><strong>Highly customizable</strong></li><li><strong>Animations and many options</strong></li></ul><p><a href="https://prc5.github.io/react-zoom-pan-pinch/" rel="noopener noreferrer" target="_blank" style="color: rgb(255, 255, 250);">Demo</a></p><p><a href="https://github.com/prc5/react-zoom-pan-pinch/" rel="noopener noreferrer" target="_blank">Github</a></p><h2>Install</h2><pre class="ql-syntax" spellcheck="false">npm install <span class="hljs-attr">--save</span> react-zoom-pan-pinch
</pre><p>OR</p><pre class="ql-syntax" spellcheck="false">yarn add react-zoom-pan-pinch
</pre><h2>Usage</h2><pre class="ql-syntax" spellcheck="false"><span class="hljs-keyword">import</span> <span class="hljs-title class_">React</span>, { <span class="hljs-title class_">Component</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">"react"</span>;
<span class="hljs-keyword">import</span> { <span class="hljs-title class_">TransformWrapper</span>, <span class="hljs-title class_">TransformComponent</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">"react-zoom-pan-pinch"</span>;

<span class="hljs-keyword">class</span> <span class="hljs-title class_">Example</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">Component</span> {
  <span class="hljs-title function_">render</span>() {
    <span class="hljs-keyword">return</span> (
      <span class="hljs-tag">&lt;<span class="hljs-name">TransformWrapper</span>&gt;&lt;<span class="hljs-name">TransformComponent</span>&gt;&lt;<span class="hljs-name">img</span> <span class="hljs-attr">src</span>=<span class="hljs-string">"image.jpg"</span> <span class="hljs-attr">alt</span>=<span class="hljs-string">"test"</span> /&gt;&lt;/<span class="hljs-name">TransformComponent</span>&gt;&lt;/<span class="hljs-name">TransformWrapper</span>&gt;</span>
    );
  }
}
</pre><p>OR</p><pre class="ql-syntax" spellcheck="false"><span class="hljs-keyword">import</span> <span class="hljs-title class_">React</span>, { <span class="hljs-title class_">Component</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">"react"</span>;
<span class="hljs-keyword">import</span> { <span class="hljs-title class_">TransformWrapper</span>, <span class="hljs-title class_">TransformComponent</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">"react-zoom-pan-pinch"</span>;

<span class="hljs-keyword">class</span> <span class="hljs-title class_">Example</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">Component</span> {
  <span class="hljs-title function_">render</span>() {
    <span class="hljs-keyword">return</span> (
      &lt;<span class="hljs-title class_">TransformWrapperdefaultScale</span>={<span class="hljs-number">1</span>}defaultPositionX={<span class="hljs-number">200</span>}defaultPositionY={<span class="hljs-number">100</span>}
      &gt;
        {<span class="hljs-function">(<span class="hljs-params">{ zoomIn, zoomOut, resetTransform, ...rest }</span>) =&gt;</span> (
          <span class="hljs-tag">&lt;<span class="hljs-name">React.Fragment</span>&gt;&lt;<span class="hljs-name">div</span> <span class="hljs-attr">className</span>=<span class="hljs-string">"tools"</span>&gt;&lt;<span class="hljs-name">button</span> <span class="hljs-attr">onClick</span>=<span class="hljs-string">{zoomIn}</span>&gt;</span>+<span class="hljs-tag">&lt;/<span class="hljs-name">button</span>&gt;&lt;<span class="hljs-name">button</span> <span class="hljs-attr">onClick</span>=<span class="hljs-string">{zoomOut}</span>&gt;</span>-<span class="hljs-tag">&lt;/<span class="hljs-name">button</span>&gt;&lt;<span class="hljs-name">button</span> <span class="hljs-attr">onClick</span>=<span class="hljs-string">{resetTransform}</span>&gt;</span>x<span class="hljs-tag">&lt;/<span class="hljs-name">button</span>&gt;&lt;/<span class="hljs-name">div</span>&gt;&lt;<span class="hljs-name">TransformComponent</span>&gt;&lt;<span class="hljs-name">img</span> <span class="hljs-attr">src</span>=<span class="hljs-string">"image.jpg"</span> <span class="hljs-attr">alt</span>=<span class="hljs-string">"test"</span> /&gt;&lt;<span class="hljs-name">div</span>&gt;</span>Example text<span class="hljs-tag">&lt;/<span class="hljs-name">div</span>&gt;&lt;/<span class="hljs-name">TransformComponent</span>&gt;&lt;/<span class="hljs-name">React.Fragment</span>&gt;</span>
        )}
      &lt;/<span class="hljs-title class_">TransformWrapper</span>&gt;
    );
  }
}
</pre><h2>Props of TransformWrapper</h2><p>PropsDefaultTypescale1numberpositionXautonumberpositionYautonumberdefaultPositionXnullnumberdefaultPositionYnullnumberdefaultScalenullnumberoptions{...}objectwheel{...}objectpan{...}objectpinch{...}objectzoomIn{...}objectzoomOut{...}objectdoubleClick{...}objectreset{...}objectscalePadding{...}objectonWheelStartnullFunctiononWheelnullFunctiononWheelStopnullFunctiononPanningStartnullFunctiononPanningnullFunctiononPanningStopnullFunctiononPinchingStartnullFunctiononPinchingnullFunctiononPinchingStopnullFunctiononZoomChangenullFunctionenablePaddingtrueBooleanenablePanPaddingtrueBoolean</p><h4>Options prop elements</h4><p>PropsDefaultTypedisabledfalsebooleantransformEnabledtruebooleanminPositionXnullnull, numbermaxPositionXnullnull, numberminPositionYnullnull, numbermaxPositionYnullnull, numberminScale1numbermaxScale8numberlimitToBoundstruebooleanlimitToWrapperfalsebooleancenterContenttrueboolean</p><h4>scalePadding prop elements</h4><p>PropsDefaultTypedisabledfalsebooleansize0.45numberanimationTime200numberanimationTypeeaseOutstring</p><h4>Wheel prop elements</h4><p>PropsDefaultTypedisabledfalsebooleanstep6.5numberwheelEnabledtruebooleantouchPadEnabledtruebooleanlimitsOnWheeltrueboolean</p><h4>Pan prop elements</h4><p>PropsDefaultTypedisabledfalsebooleandisableOnTarget[]array of class names or node tags (div,span...)lockAxisXfalsebooleanlockAxisYfalsebooleanvelocityfalsebooleanvelocityEqualToMovefalsebooleanvelocitySensitivity1numbervelocityMinSpeed1.2numbervelocityBaseTime1800numbervelocityAnimationTypeeaseOutstringpaddingtruebooleanpaddingSize40numberanimationTime200numberanimationTypeeaseOutstring</p><h4>Pinch prop elements</h4><p>PropsDefaultTypedisabledfalseboolean</p><h4>zoomIn prop elements</h4><p>PropsDefaultTypedisabledfalsebooleanstep70numberanimationtruebooleananimationTime200numberanimationTypeeaseOutstring</p><h4>zoomOut prop elements</h4><p>PropsDefaultTypedisabledfalsebooleanstep70numberanimationtruebooleananimationTime200numberanimationTypeeaseOutstring</p><h4>doubleClick prop elements</h4><p>PropsDefaultTypedisabledfalsebooleanstep70numberanimationtruebooleananimationTime200numberanimationTypeeaseOutstringmodezoomInzoomIn / zoomOut / reset</p><h4>reset prop elements</h4><p>PropsDefaultTypedisabledfalsebooleananimationtruebooleananimationTime200numberanimationTypeeaseOutstring</p><h4>Animations types</h4><p>ValueeaseOutlineareaseInQuadeaseOutQuadeaseInOutQuadeaseInCubiceaseOutCubiceaseInOutCubiceaseInQuarteaseOutQuarteaseInOutQuarteaseInQuinteaseOutQuinteaseInOutQuint</p><h4>Double click modes</h4><p>ValuezoomInzoomOutreset</p><h2>Values returned from TransformWrapper component</h2><p>ValueDescriptionTypesetScale(scale, animationTime, animationType)Sets scaleNumbersetPositionX(positionX, animationTime, animationType)Sets position xNumbersetPositionY(positionY, animationTime, animationType)Sets position yNumberzoomIn()Zooming in function, used for controls button---zoomOut()Zooming out function, used for controls button---setTransform(positionX, positionY, scale, animationTime, animationType)Sets transformations of contentNumber or nullresetTransform()Reset transformations to the initial valuesNumber</p><h2>License</h2><p>MIT ©&nbsp;<a href="https://github.com/prc5" rel="noopener noreferrer" target="_blank">prc5</a></p><p>That's it. Feel free to leave a comment.</p>

React library to support easy Zoom, Pan, Pinch on various html dom elements like Images and Div's. It is a Super fast and light react npm package...

React library to implement Zoom, Pan, Pinch on HTML Elements - TCMHACK

React library to implement Zoom, Pan, Pinch on HTML Elements

<figure class="wp-block-image size-large is-resized"><img src="https://tcmhack.in/wp-content/uploads/2021/05/react-indiana-scroll.gif" alt="" class="wp-image-841" width="472" height="265"/><figcaption>react-indiana-drag-scroll</figcaption></figure>



<p>In this example we will show how to implement the component scrolling via mouse drag &amp; drop like Google Map, Google Earth, Figma etc.</p>



<p>To implement the scrolling we will use the <code><span class="highlight"><a href="https://github.com/Norserium/react-indiana-drag-scroll" target="_blank" rel="noreferrer noopener">react-indiana-drag-scroll</a></span></code> library which is great library to Implement scroll on drag.</p>



<p>So let's get started.</p>



<h2>Demo</h2>



<p>Try it yourself! Go to <a href="https://norserium.github.io/react-indiana-drag-scroll/" target="_blank" rel="noreferrer noopener">demo website</a>  / <a href="https://codesandbox.io/s/react-indiana-drag-scroll-default-iw9xh" target="_blank" rel="noreferrer noopener">sandbox</a></p>



<h2>Install</h2>



<pre class="wp-block-code"><code>npm install --save react-indiana-drag-scroll</code></pre>



<p>or install via yarn</p>



<pre class="wp-block-code"><code>yarn add react-indiana-drag-scroll</code></pre>



<h2>Usage</h2>



<pre class="wp-block-code"><code>import React, { Component } from 'react';
import ScrollContainer from 'react-indiana-drag-scroll';
class Example extends Component {
    render () {
        return (
            &lt;ScrollContainer className="scroll-container">
                { ... }
            &lt;/ScrollContainer>
        )
    }
}</code></pre>



<h2>Component properties</h2>



<figure class="wp-block-table"><table><thead><tr><th>Prop</th><th>Type</th><th>Description</th><th>Default</th></tr></thead><tbody><tr><td>vertical</td><td>Bool</td><td>Allow vertical drag scrolling</td><td>true</td></tr><tr><td>horizontal</td><td>Bool</td><td>Allow horizontal drag scrolling</td><td>true</td></tr><tr><td>hideScrollbars</td><td>Bool</td><td>Hide the scrollbars</td><td>true</td></tr><tr><td>activationDistance</td><td>Number</td><td>The distance that distinguish click and drag start</td><td>10</td></tr><tr><td>children</td><td>Node</td><td>The content of scrolling container</td><td></td></tr><tr><td>onScroll</td><td>Function</td><td>Invoked when user scrolling container</td><td></td></tr><tr><td>onEndScroll</td><td>Function</td><td>Invoked when user ends scrolling container</td><td></td></tr><tr><td>onStartScroll</td><td>Function</td><td>Invoked when user starts scrolling container</td><td></td></tr><tr><td>onClick</td><td>Function</td><td>Invoked when user clicks the scrolling container without dragging</td><td></td></tr><tr><td>component</td><td>String</td><td>The component used for the root node.</td><td>'div'</td></tr><tr><td>className</td><td>String</td><td>The custom classname for the container</td><td></td></tr><tr><td>style</td><td>Number</td><td>The custom styles for the container</td><td></td></tr><tr><td>innerRef</td><td>ElementType</td><td>The ref to the root node (experimental alternative to&nbsp;<code>getElement</code>)</td><td></td></tr><tr><td>ignoreElements</td><td>String</td><td>Selector for elements that should not trigger the scrolling behaviour (for example,&nbsp;<code>".modal, dialog"</code>&nbsp;or&nbsp;<code>"*[prevent-drag-scroll]"</code>)</td><td></td></tr><tr><td>nativeMobileScroll</td><td>Bool</td><td>Use native mobile drag scroll for mobile devices</td><td>true</td></tr></tbody></table></figure>



<h2>Static functions</h2>



<figure class="wp-block-table"><table><thead><tr><th>Name</th><th>Returns</th><th>Description</th></tr></thead><tbody><tr><td>getElement</td><td>HTMLElement</td><td>Returns the HTML element</td></tr></tbody></table></figure>



<h2>How to set the initial scroll?</h2>



<p>To set initial scroll you need get the ref to the root node of the <code>ScrollContainer</code>. It can be implemented by <a href="https://codesandbox.io/s/react-indiana-drag-scroll-initial-scroll-innerref-0g8v5?file=/index.js" target="_blank" rel="noreferrer noopener nofollow">using <code>innerRef</code>property</a> or <a href="https://codesandbox.io/s/react-indiana-drag-scroll-initial-scroll-getelement-99o6q" target="_blank" rel="noreferrer noopener nofollow">the static function <code>getElement</code></a>. At the worst you can use the <a href="https://codesandbox.io/s/react-indiana-drag-scroll-initial-scroll-finddomnode-dvdop" target="_blank" rel="noreferrer noopener nofollow"><code>ReactDOM.findDOMNode</code></a> method.</p>



<h2>License</h2>



<p>The source code is licensed under MIT, all images (except <a href="https://www.freepik.com/free-vector/ancient-egypt-hieroglyphics-background-with-flat-design_2754100.htm" target="_blank" rel="noreferrer noopener nofollow">hieroglyphs</a>) are copyrighted to their respective owner © <a href="https://github.com/norserium" target="_blank" rel="noreferrer noopener">Norserium</a></p>



<p>That's it. Feel free to leave a comment below.</p>

react-indiana-drag-scroll



In this example we will show how to implement the component scrolling via mouse drag &amp; drop like Google Map, Goo...

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