array.md

Array - CRUD Operations

	Syntax	Example
Create
	arrName = [] // Array literal/shorthand	let fruits = ['Apple',{name:'Mango'},'Orange',function(){alert('Pineapple')}];
	arrName = new Array() // Array constructor	let arr = new Array();
Read
	arrName[index]	fruits[0];//Apple
	arrName[index].objKey // Access object	fruits[1].name; // Mango
Update
Replace	arrName[index]=value	fruits[2]='Guava'; //['Apple',{name:'Mango'},'Guava',function(){alert('Pineapple')}]
	arrName.splice(start,end,value)	fruits.splice(0,1,'Mosambi'); //['Mosambi',{name:'Mango'},'Guava',function(){alert('Pineapple')}]
Add	arrName[index]=value	fruits[4]='Orange'; //['Mosambi',{name:'Mango'},'Guava',function(){alert('Pineapple')},'Orange']
	arrName.push(value)// Add last element	fruits.push('Grapes'); //['Mosambi',{name:'Mango'},'Guava',function(){alert('Pineapple')},'Orange','Grapes']
	arrName.unshift(value)// Add first element	fruits.unshift('Banana'); //['Banana','Mosambi',{name:'Mango'},'Guava',function(){alert('Pineapple')},'Orange','Grapes']
	arrName.splice(start,0,value)// add to specific index	fruits.splice(1,0,'Apple'); //['Banana','Apple','Mosambi',{name:'Mango'},'Guava',function(){alert('Pineapple')},'Orange','Grapes']
Delete
Delete array elements	delete arrName[index]	delete fruits[0]; // [empty,'Apple','Mosambi',{name:'Mango'},'Guava',function(){alert('Pineapple')},'Orange','Grapes']
	arrName.pop() // delete last element	fruits.pop(); // [empty,'Apple','Mosambi',{name:'Mango'},'Guava',function(){alert('Pineapple')},'Orange']
	arrName.shift() // delete first element	fruits.shift(); // ['Apple','Mosambi',{name:'Mango'},'Guava',function(){alert('Pineapple')},'Orange']
	arrName.splice(start,end)// delete specific element(s)	fruits.splice(4,1); // ['Apple','Mosambi',{name:'Mango'},'Guava','Orange']
	arrName.length=length // truncates array	fruits.length=2; // ['Apple','Mosambi'];
Delete/Reset entire array	arrName.length=0	fruits.length=0; // []
	arrName=[]	fruits=[];
	arrName.splice(start,arrayLength)	fruits.splice(0,fruits.length);`

Array Iteration Methods

Syntax	Example
arrName.forEach(callback[, this]) // calls a function for each array element but returns undefined	let arr = [1,2,3]; arr.forEach(item=>console.log(item));
arrName.map(callback[, initialvalue]) // returns a new manipulated array	let arr = [1,2,3,4,5]; arr.map(item=>item*item); //[1,4,9]
arrName.keys() // returns a new array iterator object with array indices	for(let key of arr){ console.log(key)}; // 0 1 2
arrName.values() // returns a new array iterator object with array values	for(let value of arr.values()){console.log(value)}; //1 2 3
arrName.entries() // // returns a new array iterator object with array indices and values	for(let [index,value] of arr.entries()){console.log(index,value)}; 0 1 1 2 2 3
arrName.find(callback[, this]) // returns first value that satisfies condition	arr.find(item=>item>1);//2
arrName.filter(callback[, this]) // returns an array that satisfies condition	arr.filter(item=>item>1);//[2,3]
arrName.every(callback[, this]) // returns true if all elements in the array satisfy the condition	arr.some(item=>item>1);//true
arrName.some(callback[, this]) // returns true if atleast one element in the array satisfy the condition	arr.every(item=>item>1);//false

Other Array Transformation/Mutator methods

Syntax	Example
arr.sort() // returns sorted array	[1,3,2].sort(); //[1,2,3]
arr.reverse // returns reversed array	[1,2,3].reverse(); //[3,2,1]
arr.split(separator) // splits string to array	"2-3-4".split('-'); //["2", "3", "4"]
arr.join(separator) // reverse of split - joins array elements as a string	[1,2,3].join("-"); //"1-2-3"
arr.reduce((accumulator,item,index,array) =>{},initial) // reduces array to one single value	[1,2,3].reduce((x,i)=>x+i,0); //6

Other Array methods/Properties

Syntax	Example
arr.length // returns length of the array instance	[1,2,3].length; // 3
arr.toString() // returns comma separated string	[1,2,3].toString(); // "1,2,3"
arr.splice(start,end) // returns shallow copy in a new array - unlike splice, does not mutate array	[1,2,3].slice(0,1); // [1]
arr.concat(val1,val2[,...valN]) // concatenates values to array when Symbol.isConcatSpreadable is true	[1,2,3].concat(4,5); // [1, 2, 3, 4, 5]
arr.indexOf(value) //returns first index of search element, else -1	[1,2,3].indexOf(2); // 2
arr.includes(value) // returns boolean for searched result	[1,2,3].includes(2); // true
arr.find(callback[, this]) //returns first element that satisfies condition	[1,2,3].find(x=> x>1); // 2
arr.filter(callback[, this]) //returns the array that satisfies condition	[1,2,3].filter(x=> x>1); // [2, 3]
Array.isArray(arr); // Global object method - checks if value is of type array	Array.isArray({a:1}); // false
let arr=[val1,val2]; let [x,y]=arr // Array destructuring - unpack array as variables	let arr =["a","b"]; let [x,y]=arr; console.log(x,y); // a b
let [name1,name2, ...rest]= [val1,val2,..valN] //...Rest operator assigns values after … as an array	let [x,y,...rest]=[1,2,3,4,5]; console.log(rest[0]); //3

Common functionalities

Operation	Syntax/Example
Remove duplicates from array	arr.filter((a,b)=>arr.indexOf(a)===b)
Sort Integer Array	arr.sort((a,b)=>b-a);
Swap variables with array destructuring	let a='Apple', b='Banana'; [a,b]=[b,a]; console.log(a,b); // Banana Apple