JavaScript-snippets

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No.	Questions
1	Generate a random number in a given range
2	Find the difference between two arrays
3	Convert truthy/falsy to boolean(true/false)
4	Repeat a string
5	Check how long an operation takes
6	Two ways to remove an item in a specific in an array
7	Did you know you can flat an array?
8	Get unique values in an array
9	Copy Text to Clipboard
10	Nested Destructuring
11	URLSearchParams
12	Count elements in an array
13	Aliases with JavaScript Destructuring
14	The Object.is() method determines whether two values are the same value
15	Freeze an object
16	Printing Object keys and values
17	Capture the right click event
18	In HTML5, you can tell the browser when to run your JavaScript code
19	Nullish coalescing operator
20	Optional chaining
21	globalThis
22	The second argument of JSON.stringify lets you cherry-pick 🍒 keys to serialize.
23	Fire an event listener only once.
24	Vanilla JS toggle
25	Check if a string is a valid JSON
26	getBoundingClientRect
27	Check if a node is in the viewport
28	Notify when element size is changed
29	Detect if Browser Tab is in the view
30	Private class methods and fields
31	Preventing paste into an input field
32	The void operator
33	replaceAll
34	Required Function Params
35	Get input value as a number
36	reduceRight
37	Abort Fetch
38	How to change the value of an object which is inside an array
39	Numeric separators allow us to improve our code readability
40	pay attention when using every
41	How to convert an array of key-value tuples into an object
42	Native text to speech JS
43	toFixed

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How to generate a random number in a given range

// Returns a random number(float) between min (inclusive) and max (exclusive) 

const getRandomNumber = (min, max) => Math.random() * (max - min) + min;

getRandomNumber(2, 10)

 // Returns a random number(int) between min (inclusive) and max (inclusive)

const getRandomNumberInclusive =(min, max)=> {
    min = Math.ceil(min);
    max = Math.floor(max);
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

getRandomNumberInclusive(2, 10);

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How to find the difference between two arrays

const firstArr = [5, 2, 1];
const secondArr = [1, 2, 3, 4, 5];

const diff = [
    ...secondArr.filter(x => !firstArr.includes(x)),					
    ...firstArr.filter(x => !secondArr.includes(x))
];
console.log('diff',diff) //[3,4]


function arrayDiff(a, b) {
    return [
        ...a.filter(x => b.indexOf(x) === -1),
        ...b.filter(x => a.indexOf(x) === -1)
    ]
}
console.log('arrayDiff',arrayDiff(firstArr, secondArr)) //[3,4]




const difference = (a, b) => {
    const setA = new Set(a);
    const setB = new Set(b);

    return [
        ...a.filter(x => !setB.has(x)),
        ...b.filter(x => !setA.has(x))

    ]
};

difference(firstArr, secondArr); //[3,4]
console.log('difference',difference(firstArr, secondArr))

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Convert truthy falsy to boolean

const myVar = null; 
const mySecondVar = 1; 

console.log( Boolean(myVar) ) // false
console.log( !!myVar ) // false


console.log( Boolean(mySecondVar) ) // true
console.log( !!mySecondVar ) // true

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Repeat a string

let aliens = '';

for(let i = 0 ; i < 6 ; i++){
 aliens += '👽'
}
//👽👽👽👽👽👽

Array(6).join('👽')
//👽👽👽👽👽👽


'👽'.repeat(6)
//👽👽👽👽👽👽

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Check how long an operation takes

//The performance.now() method returns a DOMHighResTimeStamp, measured in milliseconds.
//performance.now() is relative to page load and more precise in orders of magnitude. 
//Use cases include benchmarking and other cases where a high-resolution time is required 
//such as media (gaming, audio, video, //etc.)

var startTime = performance.now();
doSomething();
const endTime = performance.now();
console.log("this doSomething took " + (endTime - startTime) + " milliseconds.");

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Two ways to remove an item in a specific in an array

//Mutating way
const muatatedArray = ['a','b','c','d','e'];
muatatedArray.splice(2,1)
console.log(muatatedArray) //['a','b','d','e']

//Non-mutating way
const nonMuatatedArray = ['a','b','c','d','e'];
const newArray = nonMuatatedArray.filter((item, index) => !( index === 2 ));
console.log(newArray) //['a','b','d','e']

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Did you know you can flat an array

const myArray = [2, 3, [4, 5],[7,7, [8, 9, [1, 1]]]];

myArray.flat() // [2, 3, 4, 5 ,7,7, [8, 9, [1, 1]]]

myArray.flat(1) // [2, 3, 4, 5 ,7,7, [8, 9, [1, 1]]]

myArray.flat(2) // [2, 3, 4, 5 ,7,7, 8, 9, [1, 1]]

//if you dont know the depth of the array you can use infinity
myArray.flat(infinity) // [2, 3, 4, 5 ,7,7, 8, 9, 1, 1];

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Get unique values in an array

const numbers = [1,1,3,2,5,3,4,7,7,7,8];

//Ex1
const unieqNumbers = numbers.filter((v,i,a) => a.indexOf(v )=== i )
console.log(unieqNumbers) //[1,3,2,5,4,7,8]

//Ex2
const unieqNumbers2 = Array.from(new Set(numbers))
console.log(unieqNumbers2) //[1,3,2,5,4,7,8]

//Ex3
const unieqNumbers3 = [...new Set(numbers)]
console.log(unieqNumbers3) //[1,3,2,5,4,7,8]

//EX4 lodash
const unieqNumbers4 = _.uniq(numbers)
console.log(unieqNumbers4) //[1,3,2,5,4,7,8]

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Copy Text to Clipboard

function copyToClipboard() {

  const copyText = document.getElementById("myInput");
  copyText.select();
  document.execCommand("copy");
  
}
//new API
function copyToClipboard(){
 navigator.clipboard.writeText(document.querySelector('#myInput').value)
}

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Nested Destructuring

const user = {
 id: 459,
 name: 'JS snippets',
 age:29,
 education:{
  degree: 'Masters'
 }
}

const { education : { degree } } = user;
console.log(degree) //Masters

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URLSearchParams

//The URLSearchParams interface defines utility methods to work with the query string of a URL.

const urlParams = new URLSearchParams("?post=1234&action=edit");

console.log(urlParams.has('post')); // true
console.log(urlParams.get('action')); // "edit"
console.log(urlParams.getAll('action')); // ["edit"]
console.log(urlParams.toString()); // "?post=1234&action=edit"
console.log(urlParams.append('active', '1')); // "?post=1234&action=edit&active=1"

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Count elements in an array

const myFruits = ['Apple','Orange','Mango','Banana','Apple','Apple','Mango']

//first option
const countMyFruits = myFruits.reduce((countFruits,fruit) => {
  countFruits[fruit] = ( countFruits[fruit] || 0 ) +1;
  return countFruits
 },{} )
 console.log(countMyFruits)
 // { Apple:3, Banana:1, Mango:2, Orange:1 }
 
 //seconf option
 const fruitsCounter = {};
 
 for( const fruit of myFruits ){
   fruitsCounter[fruit] = fruitsCounter[fruit] ? fruitsCounter[fruit]+1 :1;
 }
  
 console.log(fruitsCounter)
 // { Apple:3, Banana:1, Mango:2, Orange:1 }

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Aliases with JavaScript Destructuring

//There are cases where you want the destructured variable to have a different name than the property name

const obj = { 
  name: "JSsnippets"													
};


// Grabs obj.name as { pageName }
const { name: pageName } = obj;

//log our alias
console.log(pageName) // JSsnippets

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The Object.is() method determines whether two values are the same value

Object.is('foo', 'foo');     // true

Object.is(null, null);       // true

Object.is(Nan, Nan);       // true 😱

const foo = { a: 1 };
const bar = { a: 1 };
Object.is(foo, foo);         // true
Object.is(foo, bar);         // false

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Freeze an object

const obj = { 
  name: "JSsnippets",
  age:29,
  address:{
	  street : 'JS'
	}
};														

const frozenObject = Object.freeze(obj);

frozenObject.name = 'weLoveJS'; // Uncaught TypeError

//Although, we still can change a property’s value if it’s an object:

frozenObject.address.street = 'React'; // no error, new value is set


delete frozenObject.name // Cannot delete property 'name' of #<Object>


//We can check if an object is frozen by using
Object.isFrozen(obj) //true

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Printing Object keys and values

const obj = { 
  name: "JSsnippets",
  age:29,
};

//Object.entries() method is used to return an array consisting of enumerable property 
//[key, value] pairs of the object which are passed as the parameter.

for(let [key,value] of Object.entries(obj)){
   console.log(`${key}: ${value}`)
}

//expected output:
// "name: Jssnippets"
// "age: 29"
// order is not guaranteed

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Capture the right click event

window.oncontextmenu = () => {
	console.log('right click');
	return false // cancel default menu
}
//or

window.addEventListener('contextmenu', ()=>{
	console.log('right click');
	return false // cancel default menu
},false)

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In HTML5, you can tell the browser when to run your JavaScript code

//Without async or defer, browser will run your script immediately, before rendering the elements that's below your script tag.
<script src="myscript.js"></script>

//With async (asynchronous), browser will continue to load the HTML page and render it while the browser load and execute the script at the same time.
//Async is more useful when you really don't care when the script loads and nothing else that is user dependent depends upon that script loading.(for scripts likes Google analytics)
<script async src="myscript.js"></script>

//With defer, browser will run your script when the page finished parsing. (not necessary finishing downloading all image files. 
<script defer src="myscript.js"></script>

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Nullish coalescing operator

// an equality check against nullary values (e.g. null or undefined). Whenever the expression to the left of the ?? operator evaluates to either //undefined or null, the value defined to the right will be returned.

const foo = undefined ?? 'default string';
console.log(foo);
// expected output: "default string"


const age = 0 ?? 30;
console.log(age);
// expected output: "0"

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Optional chaining

const car = {}
const carColor = car.name.color
console.log(carColor);
// error- "Uncaught TypeError: Cannot read property 'carColor' of undefined		

//In JavaScript, you can first check if an object exists, and then try to get one of its properties, like this:
const carColor = car && car.name && car.name.color;
console.log(carColor);
//undefined- no error


//Now this new optional chaining operator will let us be even more fancy:

const newCarColor = car?.name?.color;
console.log(newCarColor) 
//undefined- no error
					
//You can use this syntax today using @babel/plugin-proposal-optional-chaining

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globalThis

Accessing the global property in JavaScript has always posed some difficulty. This is because 
different platforms have different ways to access it.

Client-side JavaScript uses window or self

Node.js uses global

Web workers use self

The globalThis property provides a standard way of accessing the global 'this' value across environments. you can access the global object in a consistent manner without having to know which environment the code is being run in. 

console.log(globalThis) //get the global this depends on your environment

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The second argument of JSON.stringify lets you cherry-pick 🍒 keys to serialize.

const user = {
 id: 459,
 name: 'JS snippets',
 age:29,
 education:{
  degree: 'Masters'
 }
}

JSON.stringify(user,[name,age], 2)						

/*
returns

{
  "name": "JS snippets",
  "age": 29
}


*/

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Fire an event listener only once

const el = document.getElementById("btn");

function myClickHandler(){
  console.log('this click will only fire once')
}


el.addEventListener('click', myClickHandler, {
  once: true,
});

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Vanilla JS toggle

const span = document.querySelector("span");
let classes = span.classList;

span.addEventListener("click", function() {
  let result = classes.toggle("active");

  if (result) {
    console.log("active class was added");
  } else {
    console.log("active class was removed");
  }
});

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Check if a string is a valid JSON

function isJson(str) {
    try {
        JSON.parse(str);
    } catch (e) {
      //the json is  not ok
        return false;
    }
    //the json is ok
    return true;									
}

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getBoundingClientRect

//getBoundingClientRect provides you with important pieces of data about an
//HTML element’s size and positioning.

const bodyBounderies = document.body.getBoundingClientRect();
// =>  {
//       top: Number,
//       left: Number,
//       right: Number,
//       bottom: Number,
//       x: Number,
//       y: Number,
//       width: Number,
//       height: Number,
//     }

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Check if a node is in the viewport

bonus: add/remove animation depending if an image is in the viewport https://codepen.io/JSsnippets/pen/PoqrjEY

const image = document.querySelector('.animate-me');

observer = new IntersectionObserver((entries) => {
  const [ myImg ] = entries;
    if (myImg.intersectionRatio > 0) {
      myImg.target.classList.add('fancy');
    } else {
      myImg.target.classList.remove('fancy');
    }
});


observer.observe(image);

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Notify when element size is changed

see our codepen: https://codepen.io/JSsnippets/pen/dyYoYVX

const foo = document.getElementById("foo");

const observer = new ResizeObserver((entries) => {
  for (let entry of entries) {
    const cr = entry.contentRect;
    console.log = `Size: ${cr.width}px X ${cr.height}px`;
  }
});
observer.observe(foo);

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Detect if Browser Tab is in the view

play/pause video accordingly see our codepen: https://codepen.io/JSsnippets/pen/gOapPzq

const video =  document.getElementById("my-video");

const onVisibilitychange =()=>{
   return document.hidden 
     ? video.pause() 
     : video.play();
} 

document.addEventListener("visibilitychange", onVisibilitychange)

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Private class methods and fields

class Students {
  #name;

  constructor(){
    this.#name = "JS snippets";
  }

  #privateMethod() {
    return 'Come and learn Js with us';
  }

  getPrivateMessage() {
      return this.#privateMethod();
  }
}

const instance = new Something();
console.log(instance.name); //=> undefined
console.log(instance.privateMethod); //=> undefined
console.log(instance.getPrivateMessage()); //=> Come and learn Js with us

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Preventing paste into an input field

see our codepen: https://codepen.io/JSsnippets/pen/qBbyMoJ

const pasteBox = document.getElementById("paste-no-event");
pasteBox.onpaste = (e) => {
  e.preventDefault();
  return false;
};

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The void operator

The void operator evaluates the given expression and then returns undefined.

void 0;  		//returns undefined
void (0); 		//returns undefined
void {}; 		//returns undefined
void "JSsnippets; 	//returns undefined
void (0); 		//returns undefined
void (2 == '2'); 	//returns undefined
void anyfunction(); 	//returns undefined

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replaceAll

the method string.replaceAll(search, replaceWith) replaces all appearances of search string with replaceWith.

const str = 'this is a JSsnippets example';

const updatedStr = str.replace('example', 'snippet'); // 'this is a  JSsnippets snippet'


The tricky part is that replace method replaces only the very first match of the substring we have passed:


const str = 'this is a JSsnippets example and examples are great';

const updatedStr = str.replace('example', 'snippet'); //'this is a JSsnippets snippet and examples are great'

In order to go through this, we need to use a global regexp instead:


const str = 'this is a JSsnippets example and examples are great';

const updatedStr = str.replace(/example/g, 'snippet'); //'this is a JSsnippets snippet and snippets are greatr'

but now we have new friend in town, replaceAll

const str = 'this is a JSsnippets example and examples are great';

const updatedStr = str.replaceAll('example', 'snippet'); //'this is a JSsnippets snippet and snippets are greatr'

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Required Function Params

Expanding on the default parameter technique, we can mark a parameter as mandatory

const isRequired = () => {
    throw new Error( 'This is a mandatory parameter.' );
}


const getPage = ( pageName = 'Jssnippets', url = isRequired() ) => {
    return `${pageName} ${url}`;
}

console.log(getPage());

//In the above code, url will be undefined and that will try to set the default value for it which is the isRequired() function. It will throw an error as,

//Uncaught error: This is a mandatory parameter.
//at isRequired

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Get input value as a number

<input type="number" id="JSsnippets" onkeyup="checkMyType(event)" />

function checkMyType(event){
  
  console.log(typeof event.target.value) // string
  console.log(typeof event.target.valueAsNumber ) // number

}

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reduceRight

const arr = ["a", "b", "c", "d", "e"]

const reduceArray = arr.reduce((acc, current) => {
    return acc + current
}, "")
//return abcde

const reduceRightArray = arr.reduceRight((acc, current) => {
    return acc + current
}, "")
//return edcba

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Abort Fetch

//HTML
<button id="download">Download</button>
<button id="abort">Abort</button>

//JS
let controller;

document.querySelector('#download').addEventListener('click', () => {
  controller = new AbortController();
  const signal = controller.signal;
  fetch('https://cdn.plyr.io/static/demo/View_From_A_Blue_Moon_Trailer-576p.mp4', {signal})
    .then(() => console.log('done'));
});

document.querySelector('#abort').addEventListener('click', function() {
  controller.abort();
});

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How to change the value of an object which is inside an array

const state = [
  {
    userId: 1,
    name: "JSSnippets",
    isOwner: false,
  },
  {
    userId: 2,
    name: "React",
    isOwner: false,
  },
  {
    userId: 3,
    name: "Vue",
    isOwner: false,
  },
  {
    userId: 4,
    name: "Angular",
    isOwner: false,
  },
];

const newState = state.map((obj) =>
  obj.name === "JSSnippets" ? { ...obj, isOwner: true } : obj			
);

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Numeric separators allow us to improve our code readability

100_000_000 === 100000000 // true

300_000 === 300000 //true

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pay attention when using every

Calling this method on an empty array will return true for any condition!

const arr = []
const result = arr.every(x=> x==5)
console.log(result) //true

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How to convert an array of key-value tuples into an object

const JSarr = [
    ['name', 'JSsnippets'],
    ['address', 'worldwide'],
    ['year', '2018'],
    ['followers', '15000']

];

const obj = Object.fromEntries(JSarr);
//{
//  "name": "JSsnippets",
// "address": "worldwide",
//  "year": "2018",
//  "followers": "15000"
//}

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Native text to speech JS

const startSpeaking=()=>{

	let msg = document.getElementById("text-to-speech").value;
	let speech = new SpeechSynthesisUtterance();
	
	speech.lang = "en-US";
	speech.text = msg;
	speech.volume = 1;
	speech.rate = 1;
	speech.pitch = 1;

	window.speechSynthesis.speak(speech);
}

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toFixed

Warning: Floating point numbers cannot represent all decimals precisely in binary. This can lead to unexpected results, such as 0.1 + 0.2 === 0.3 returning false .

123.678.toFixed()       // Returns '124'
123.678.toFixed(1)      // Returns '123.7': Note rounding

2.35.toFixed(1)        // Returns '2.4'. Note it rounds up
2.65.toFixed(1)        // Returns '2.6'. Note it rounds down -why??? see the warning above

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