.? in javascript code example

Example 1: javascript ... operator

//The operator ... is part of the array destructuring.
//It's used to extract info from arrays to single variables.
//The operator ... means "the rest of the array".
var [head, ...tail] = ["Hello", "I" , "am", "Sarah"];
console.log(head);//"Hello"
console.log(tail);//["I", "am", "Sarah"]

//It can be used to pass an array as a list of function arguments
let a = [2,3,4];
Math.max(a) //--> NaN
Math.max(...a) //--> 4

Example 2: js !==

var x = 5;

// === 	equal value and equal type
// e.g. 1. 
x === 5 returns true

// e.g. 2.
x === "5" returns false

// !== not equal value or not equal type
// e.g. 1.
x !== 5 returns false

// e.g. 2.
x !== "5" returns true

// e.g. 3.
x !== 8 returns true