array.js

var array = [1,2,3,4,5,6]; console.log(array.slice(-1)); // [6] console.log(array.slice(-2)); // [5,6] console.log(array.slice(-3)); // [4,5,6] 

var array = [1,2,3,4,5,6]; console.log(array.length); // 6
array.length = 3; console.log(array.length); // 3 console.log(array); // [1,2,3] 

Array.push.apply(arr1, arr2) which instead creates a new array – it will merge the second array in the first one reducing the memory usage. 
var array1 = [1,2,3]; var array2 = [4,5,6]; console.log(array1.push.apply(array1, array2)); // [1,2,3,4,5,6];

NodeList to Array 
var ps=document.querySelectorAll("p");
[].slice.call(ps);

Suffle an array 
var list = [1,2,3]; console.log(list.sort(function() { Math.random() - 0.5 })); // [2,1,3]