Methods on Strings

Methods do NOT mutate the strings they're called on. They return NEW strings with the return value of the method.


Returns the character to the right of the specified index

'dog'.charAt(1) // => 'o'

.slice(num1, num2)

Returns a string from the right of the first specified index to the left of the second specified index, or the end of the string

'supercalifragilisticexpialadocious'.slice(5, 9) // => 'cali'

'supercalifragilisticexpialadocious'.slice(9) // => 'fragilisticexpialadocious'


returns a lowercase version of the string it's called on

'HeLlo'.toLowerCase() // => 'hello'


returns a capitalized version of the string it's called on

'hello'.toUpperCase() // => HELLO


returns an array of strings split at the specified character

'blueberry'.split('e') // => ['blu', 'b', 'rry']

Methods on Numbers

Numbers also have some methods that can be called on them. There is also a globally available Math class available in JavaScript which has a number of usefull methods attached to it


takes a number object and turns it into a string

let x = 10
x.toString() // => '10'

(42).toString() // => '42'

Note that you will need to assign to value of the number to a variable (or wrap it in parentheses) and then call .toString() on it otherwise you'll get SyntaxError: Invalid or unexpected token.


takes a number object and evaluatues it to a specified number of places

(7.54321768).toPrecision(4) // => 7.543


evaluates a value and returns a boolean depending on if it's a number or not

x = 10
y = 'cat'

isNaN(x) // => false
isNaN(y) // => true


trims all decimal places off a given number

Math.floor(134.97837) // => 134

Note that this does not round the number, it just trims off everything after the decimal point


returns a random number between 0 (inclusive) and one (exclusive)

Math.random() // => a random number between 0 and 0.99999999999...