JavaScript Reference

Built-in JavaScript methods and functions: strings, arrays, numbers, Math, objects, JSON and more.

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Name	Group	Description
String.length	String	The number of characters in a string.
toUpperCase()	String	Returns the string in upper case.
toLowerCase()	String	Returns the string in lower case.
trim()	String	Removes whitespace from both ends.
slice()	String	Extracts part of a string.
substring()	String	Extracts characters between two indexes.
indexOf()	String	The position of the first match, or -1.
includes()	String	Whether a string contains text.
startsWith()	String	Whether a string starts with text.
endsWith()	String	Whether a string ends with text.
replace()	String	Replaces the first match.
replaceAll()	String	Replaces every match.
split()	String	Splits a string into an array.
repeat()	String	Repeats a string.
padStart()	String	Pads the start to a length.
padEnd()	String	Pads the end to a length.
charAt()	String	The character at an index.
at()	String	The character at an index; negative counts from the end.
concat()	String	Joins strings.
match()	String	Finds matches with a regular expression.
localeCompare()	String	Compares strings for sorting.
Array.length	Array	The number of items in an array.
push()	Array	Adds items to the end.
pop()	Array	Removes and returns the last item.
shift()	Array	Removes and returns the first item.
unshift()	Array	Adds items to the start.
slice()	Array	Copies part of an array.
splice()	Array	Adds or removes items in place.
concat()	Array	Joins arrays.
join()	Array	Joins items into a string.
reverse()	Array	Reverses an array in place.
sort()	Array	Sorts an array in place.
indexOf()	Array	The first index of an item, or -1.
includes()	Array	Whether an array contains an item.
find()	Array	The first item that passes a test.
findIndex()	Array	The index of the first item that passes a test.
filter()	Array	A new array of items that pass a test.
map()	Array	A new array made by transforming each item.
reduce()	Array	Combines all items into one value.
forEach()	Array	Runs a function for each item.
some()	Array	Whether any item passes a test.
every()	Array	Whether every item passes a test.
flat()	Array	Flattens nested arrays.
flatMap()	Array	Maps then flattens one level.
fill()	Array	Fills an array with a value.
Array.isArray()	Array	Whether a value is an array.
Array.from()	Array	Makes an array from an iterable.
at()	Array	The item at an index; negative counts from the end.
Number()	Number	Converts a value to a number.
parseInt()	Number	Parses an integer from a string.
parseFloat()	Number	Parses a decimal from a string.
toFixed()	Number	Formats a number with fixed decimals.
Number.isInteger()	Number	Whether a value is an integer.
isNaN()	Number	Whether a value is NaN.
Math.round()	Math	Rounds to the nearest integer.
Math.floor()	Math	Rounds down.
Math.ceil()	Math	Rounds up.
Math.trunc()	Math	Removes the decimal part.
Math.abs()	Math	The absolute value.
Math.max()	Math	The largest of the arguments.
Math.min()	Math	The smallest of the arguments.
Math.pow()	Math	Raises to a power.
Math.sqrt()	Math	The square root.
Math.random()	Math	A random number from 0 up to (not including) 1.
Math.PI	Math	The value of pi.
Object.keys()	Object	An array of an object's property names.
Object.values()	Object	An array of an object's values.
Object.entries()	Object	An array of [key, value] pairs.
Object.assign()	Object	Copies properties into an object.
Object.freeze()	Object	Makes an object read only.
hasOwnProperty()	Object	Whether an object has its own property.
JSON.stringify()	JSON	Converts a value to JSON text.
JSON.parse()	JSON	Converts JSON text to a value.
console.log()	Console	Prints values to the console.
setTimeout()	Timers	Runs a function once after a delay.
setInterval()	Timers	Runs a function repeatedly.
Promise	Async	An object for a value that arrives later.
async / await	Async	Write asynchronous code that reads in order.
Date	Date	Works with dates and times.
Date.now()	Date	Milliseconds since 1 January 1970.
typeof	Operators	The type of a value.
Set	Collections	A collection of unique values.
Map	Collections	A collection of key-value pairs.
RegExp.test()	RegExp	Tests a string against a pattern.
structuredClone()	Global	Makes a deep copy of a value.
encodeURIComponent()	Global	Encodes text for use in a URL.