JavaScript array merging case study

var a = [1,2,3];
var b=[4,5]
a = a.concat(b);
console.log(a);
//The output here is [1, 2, 3, 4, 5]

// ES5 notation var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
Array.prototype.push.apply(arr1, arr2);
console.log(arr1) // [0, 1, 2, 3, 4, 5]

// ES6 way var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
arr1.push(...arr2);
console.log(arr1) // [0, 1, 2, 3, 4, 5]

// ES6 way var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
var arr3=[...arr1, ...arr2]
console.log(arr3) // [0, 1, 2, 3, 4, 5]