javascript.info Notes - Numbers

Quick notes about numbers in Javascript. It is expected that you have already understood how it works and just want to revise the important points.

let billion_1 = 1000000000;
let billion_2 = 1_000_000_000;
let billion_3 = 1e9; 
//all above are same and equal

//all below are same and equal
let mсs_1 = 0.000001;
let mсs_2 = 0.000_001;
let mcs_3 = 1e-6; // five zeroes to the left from 1

I am ignoring Hex, binary and octal numbers as they are rarely used. Just check the documentation if needed.

.toString(base)

let num = 255;

alert( num.toString(16) );  // ff
alert( num.toString(2) );   // 11111111

//The base can vary from 2 to 36. By default it’s 10.

Rounding

Math.floor(3.1) // 3
Math.ceil(3.1) // 4
Math.round(3.1) // 3
Math.trunc(3.1) // 3

Math.floor(3.6) // 3
Math.ceil(3.6) // 4
Math.round(3.6) // 4
Math.trunc(3.6) // 3
//check documentation if any result does not make sense

//if we’d like to round the number to n-th digit after the decimal
let pi = 3.14159265359;
pi.toFixed() // 3
pi.toFixed(1) //3.1
pi.toFixed(2) // 3.14
pi.toFixed(3)  //3.142
pi.toFixed(4) //3.1416
pi.toFixed(5) //3.14159

Note: NaN, Infinity can be tricky. Check stackoverflow if needed.

parsing numbers from string

alert( parseInt('100px') ); // 100
alert( parseFloat('12.5em') ); // 12.5

alert( parseInt('12.3') ); // 12, only the integer part is returned
alert( parseFloat('12.3.4') ); // 12.3, the second point stops the read

Misc useful Math functions:

Math.random()
//Returns a random number from 0 to 1 (not including 1).
Math.max(3, 5, -10, 0, 1) // 5
Math.min(1, 2, 3, 5) // 1
Math.pow(2, 10) // 2 ^ 10 = 1024

Refer to Math object documentation if more detail is needed.