what does ~~ mean in javscript code example

Example 1: 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

Example 2: what does -= mean in JavaScript

/* JavaScript shorthand -=
-= is shorthand to subtract something from a
variable and store the result as that same variable.
*/

// The standard syntax:
var myVar = 5; 
console.log(myVar) // 5
var myVar = myVar - 3;
console.log(myVar) // 2

// The shorthand:
var myVar = 5;
console.log(myVar) // 5
var myVar -= 3;
console.log(myVar) // 2