Table of Contents

How to generate a random number in a given range

// Returns a random number(float) between min (inclusive) and max (exclusive)constgetRandomNumber=(min,max)=>Math.random()*(max-min)+min;getRandomNumber(2,10)// Returns a random number(int) between min (inclusive) and max (inclusive)constgetRandomNumberInclusive=(min,max)=>{min=Math.ceil(min);max=Math.floor(max);returnMath.floor(Math.random()*(max-min+1))+min;}getRandomNumberInclusive(2,10);

How to find the difference between two arrays

constfirstArr=[5,2,1];constsecondArr=[1,2,3,4,5];constdiff=[    ...secondArr.filter(x=>!firstArr.includes(x)),    ...firstArr.filter(x=>!secondArr.includes(x))];console.log('diff',diff)//[3,4]functionarrayDiff(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]constdifference=(a,b)=>{constsetA=newSet(a);constsetB=newSet(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))

Convert truthy falsy to boolean

constmyVar=null;constmySecondVar=1;console.log(Boolean(myVar))// falseconsole.log(!!myVar)// falseconsole.log(Boolean(mySecondVar))// trueconsole.log(!!mySecondVar)// true

Repeat a string

letaliens='';for(leti=0;i<6;i++){aliens+='👽'}//👽👽👽👽👽👽Array(6).join('👽')//👽👽👽👽👽👽'👽'.repeat(6)//👽👽👽👽👽👽

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

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

//Mutating wayconstmuatatedArray=['a','b','c','d','e'];muatatedArray.splice(2,1)console.log(muatatedArray)//['a','b','d','e']//Non-mutating wayconstnonMuatatedArray=['a','b','c','d','e'];constnewArray=nonMuatatedArray.filter((item,index)=>!(index===2));console.log(newArray)//['a','b','d','e']

Did you know you can flat an array

constmyArray=[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 infinitymyArray.flat(infinity)// [2, 3, 4, 5 ,7,7, 8, 9, 1, 1];

Get unique values in an array

constnumbers=[1,1,3,2,5,3,4,7,7,7,8];//Ex1constunieqNumbers=numbers.filter((v,i,a)=>a.indexOf(v)===i)console.log(unieqNumbers)//[1,3,2,5,4,7,8]//Ex2constunieqNumbers2=Array.from(newSet(numbers))console.log(unieqNumbers2)//[1,3,2,5,4,7,8]//Ex3constunieqNumbers3=[...newSet(numbers)]console.log(unieqNumbers3)//[1,3,2,5,4,7,8]//EX4 lodashconstunieqNumbers4=_.uniq(numbers)console.log(unieqNumbers4)//[1,3,2,5,4,7,8]

Copy Text to Clipboard

functioncopyToClipboard(){constcopyText=document.getElementById("myInput");copyText.select();document.execCommand("copy");}//new APIfunctioncopyToClipboard(){navigator.clipboard.writeText(document.querySelector('#myInput').value)}

Nested Destructuring

constuser={id:459,name:'JS snippets',age:29,education:{degree:'Masters'}}const{education :{ degree}}=user;console.log(degree)//Masters

URLSearchParams

//The URLSearchParams interface defines utility methods to work with the query string of a URL.consturlParams=newURLSearchParams("?post=1234&action=edit");console.log(urlParams.has('post'));// trueconsole.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"

Count elements in an array

constmyFruits=['Apple','Orange','Mango','Banana','Apple','Apple','Mango']//first optionconstcountMyFruits=myFruits.reduce((countFruits,fruit)=>{countFruits[fruit]=(countFruits[fruit]||0)+1;returncountFruits},{})console.log(countMyFruits)// { Apple:3, Banana:1, Mango:2, Orange:1 }//seconf optionconstfruitsCounter={};for(constfruitofmyFruits){fruitsCounter[fruit]=fruitsCounter[fruit] ?fruitsCounter[fruit]+1 :1;}console.log(fruitsCounter)// { Apple:3, Banana:1, Mango:2, Orange:1 }

Aliases with JavaScript Destructuring

//There are cases where you want the destructured variable to have a different name than the property nameconstobj={name:"JSsnippets"};// Grabs obj.name as { pageName }const{name:pageName}=obj;//log our aliasconsole.log(pageName)// JSsnippets

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

Object.is('foo','foo');// trueObject.is(null,null);// trueObject.is(Nan,Nan);// true 😱constfoo={a:1};constbar={a:1};Object.is(foo,foo);// trueObject.is(foo,bar);// false

Freeze an object

constobj={name:"JSsnippets",age:29,address:{street :'JS'}};constfrozenObject=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 setdeletefrozenObject.name// Cannot delete property 'name' of #<Object>//We can check if an object is frozen by usingObject.isFrozen(obj)//true

Printing Object keys and values

constobj={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]ofObject.entries(obj)){console.log(`${key}:${value}`)}//expected output:// "name: Jssnippets"// "age: 29"// order is not guaranteed

Capture the right click event

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

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

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.constfoo=undefined??'default string';console.log(foo);// expected output: "default string"constage=0??30;console.log(age);// expected output: "0"

Optional chaining

constcar={}constcarColor=car.name.colorconsole.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:constcarColor=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:constnewCarColor=car?.name?.color;console.log(newCarColor)//undefined- no error//You can use this syntax today using@babel/plugin-proposal-optional-chaining

globalThis

AccessingtheglobalpropertyinJavaScripthasalwaysposedsomedifficulty.Thisisbecausedifferentplatformshavedifferentwaystoaccessit.Client-sideJavaScriptuseswindoworselfNode.jsusesglobalWebworkersuseselfTheglobalThispropertyprovidesastandardwayofaccessingtheglobal'this'valueacrossenvironments.youcanaccesstheglobalobjectinaconsistentmannerwithouthavingtoknowwhichenvironmentthecodeisbeingrunin.console.log(globalThis)//get the global this depends on your environment

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

constuser={id:459,name:'JS snippets',age:29,education:{degree:'Masters'}}JSON.stringify(user,[name,age],2)/*returns{  "name": "JS snippets",  "age": 29}*/

Fire an event listener only once

constel=document.getElementById("btn");functionmyClickHandler(){console.log('this click will only fire once')}el.addEventListener('click',myClickHandler,{once:true,});

Vanilla JS toggle

constspan=document.querySelector("span");letclasses=span.classList;span.addEventListener("click",function(){letresult=classes.toggle("active");if(result){console.log("active class was added");}else{console.log("active class was removed");}});

Check if a string is a valid JSON

functionisJson(str){try{JSON.parse(str);}catch(e){//the json is  not okreturnfalse;}//the json is okreturntrue;}

getBoundingClientRect

//getBoundingClientRect provides you with important pieces of data about an//HTML element’s size and positioning.constbodyBounderies=document.body.getBoundingClientRect();// =>  {//       top: Number,//       left: Number,//       right: Number,//       bottom: Number,//       x: Number,//       y: Number,//       width: Number,//       height: Number,//     }

Check if a node is in the viewport

constimage=document.querySelector('.animate-me');observer=newIntersectionObserver((entries)=>{const[myImg]=entries;if(myImg.intersectionRatio>0){myImg.target.classList.add('fancy');}else{myImg.target.classList.remove('fancy');}});observer.observe(image);

Notify when element size is changed

constfoo=document.getElementById("foo");constobserver=newResizeObserver((entries)=>{for(letentryofentries){constcr=entry.contentRect;console.log=`Size:${cr.width}px X${cr.height}px`;}});observer.observe(foo);

Detect if Browser Tab is in the view

constvideo=document.getElementById("my-video");constonVisibilitychange=()=>{returndocument.hidden      ?video.pause()      :video.play();}document.addEventListener("visibilitychange",onVisibilitychange)

Private class methods and fields

classStudents{  #name;constructor(){this.#name="JS snippets";}  #privateMethod(){return'Come and learn Js with us';}getPrivateMessage(){returnthis.#privateMethod();}}constinstance=newSomething();console.log(instance.name);//=> undefinedconsole.log(instance.privateMethod);//=> undefinedconsole.log(instance.getPrivateMessage());//=> Come and learn Js with us

Preventing paste into an input field

constpasteBox=document.getElementById("paste-no-event");pasteBox.onpaste=(e)=>{e.preventDefault();returnfalse;};

The void operator

void0;//returns undefinedvoid(0);//returns undefinedvoid{};//returns undefinedvoid "JSsnippets; //returns undefinedvoid(0);//returns undefinedvoid(2=='2');//returns undefinedvoidanyfunction();//returns undefined

replaceAll

conststr='this is a JSsnippets example';constupdatedStr=str.replace('example','snippet');// 'this is a  JSsnippets snippet'Thetrickypartisthatreplacemethodreplacesonlytheveryfirstmatchofthesubstringwehave passed:conststr='this is a JSsnippets example and examples are great';constupdatedStr=str.replace('example','snippet');//'this is a JSsnippets snippet and examples are great'Inordertogothroughthis,weneedtouseaglobalregexpinstead:conststr='this is a JSsnippets example and examples are great';constupdatedStr=str.replace(/example/g,'snippet');//'this is a JSsnippets snippet and snippets are greatr'butnowwehavenewfriendintown,replaceAllconststr='this is a JSsnippets example and examples are great';constupdatedStr=str.replaceAll('example','snippet');//'this is a JSsnippets snippet and snippets are greatr'

Required Function Params

constisRequired=()=>{thrownewError('This is a mandatory parameter.');}constgetPage=(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

Get input value as a number

<inputtype="number"id="JSsnippets"onkeyup="checkMyType(event)"/>functioncheckMyType(event){console.log(typeofevent.target.value)// stringconsole.log(typeofevent.target.valueAsNumber)// number}

reduceRight

constarr=["a","b","c","d","e"]constreduceArray=arr.reduce((acc,current)=>{returnacc+current},"")//return abcdeconstreduceRightArray=arr.reduceRight((acc,current)=>{returnacc+current},"")//return edcba

Abort Fetch

//HTML<buttonid="download">Download</button><buttonid="abort">Abort</button>//JSletcontroller;document.querySelector('#download').addEventListener('click',()=>{controller=newAbortController();constsignal=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();});