Rest Operator
The rest parameter syntax allows us to represent an indefinite number of arguments as an array
function add(num1,...args){ in args it will return array containing numbers
return args[0]+args[1]
}
console.log(add(1,3,5)); in args there is 3,5 so the sum will be 8
Spread Operator
It will unpack the values of a array,this method will not affect a original element but creates copy
let arr = ["a","b","c","d"]
let arr2 = ["e","f","g"]
let newarr = [...arr , ...arr2]; combine both array into new one
console.log(newarr); result===> ["a","b","c","d","e","f","g"]
newarr.push("h"); it will just push into the new array
console.log(newarr); result===> ["a","b","c","d","e","f","g","h"]
Template Literals
It is replacement to single/double quotes,it also gives facility to addd variables or do operations,start with backticks instead of quotes
var para = ` My Name is
Uzair `
console.log(para); It will include line break in result
Interpolate with backticks
Adding variables in between or performing operations
var myVariable = `test1`
${} is used to combine variable in it
var variable2 = `Something ${ myVariable }`
you can also perform operation in it
var variable3 = `sum is ${1+2+3} ` you can also perform operation in it
console.log(variable2 + variable3)
for of loop
prints all the values of list
iterates all the elements
let list = [1,2,7,4,5,6]
for(let value of list){
console.log(value);
} result ====> 123456
for in loop
it will iterate the length / index not elements
let list = [1,2,7,4,5,6]
for(i in list){
console.log(i);
} 0,1,2,3,4,5 all indexes of array
Arrow Functions
An arrow function expression is a syntactically compact alternative to a regular function expression,The fat arrows are amazing because they would make your this behave properly, i.e., this will have the same value as in the context of the function
hello = () => {
return "Hello World!";
}
Sets
A Set is a collection of unique elements
const arr = [5, 1, 5, 7, 7, 5];
const unique = [...new Set(arr)]; // [ 5, 1, 7 ]
Maps
The map() method in JavaScript creates an array by calling a specific function on each element present in the parent array.
var el = document.getElementById('root');
var arr = [2, 5, 6, 3, 8, 9];
var newArr = arr.map(function(val, index){
return {key:index, value:val*val};
})
console.log(newArr)
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