Online JavaScript
benchmark tool

Test performance
of your JavaScript code.
Generate random alphanumeric string in JavaScript (not crypto strong)
Number separated by spaces (regex vs substr)
Counting words in string
Add a class name to an element (pure js, jQuery)
getElementsByClassName vs querySelector
Create an array with random values in JavaScript
Swap two variables (tmp variable, array way, destructuring)
String to Array (split, spread, Array.from)