Few Javascript or JQuery Tricks for array and operators

 1) Empty an array

var arr = [10 , 20 , 30 ];
arr.length = 0; // arr will be equal to [].

2) Truncate an array using length

Like the previous example of emptying an array, we truncate it using the length property.

var arr = [10, 20, 30, 40, 50, 60, 70, 80, 90];
arr.length = 4; // arr will be equal to [10, 20, 30, 40].

As a bonus, if you set the array length to a higher value, the length will be changed and new items will be added with undefined as a value. The array length is not a read only property.

arr.length = 10; // the new array length is 10
arr[arr.length - 1] ; // arr [10, 20, 30, 40, 50, 60, 70, 80, 90, undefined];

3)Use logical AND/ OR for conditions

var foo = 10;
foo == 10 && doSomething(); // is the same thing as if (foo == 10) doSomething();
foo == 5 || doSomething(); // is the same thing as if (foo != 5) doSomething();

4) Comma operator

var a = 10;
var b = ( a++, 99 );
console.log(a);  // a will be equal to 10
console.log(b);  // b is equal to 99

5) Swap variables

let v1 = 'value 1';
let v2 = 'value 2';

[v1,v2] = [v2, v1];
console.log(v1, v2);