JavaScript Built-ins

Accessing, searching, extracting, replacing, and transforming text values.

Term / Syntax	Name	Description	Example
.length	String Length	Returns the number of characters in a string.	"JavaScript".length; // 10
string[index]	Character Access	Returns the character at a specified zero-based index.	"JavaScript"[0]; // "J"
.includes()	Text Check	Checks whether a string contains specified text.	"JavaScript".includes("Script"); // true
.indexOf()	Text Position	Returns the index of the first occurrence of specified text, or -1 if it is not found.	"JavaScript".indexOf("Script"); // 4
.startsWith()	Beginning Check	Checks whether a string begins with specified text.	"JavaScript".startsWith("Java"); // true
.endsWith()	Ending Check	Checks whether a string ends with specified text.	"JavaScript".endsWith("Script"); // true
.slice()	Extract Text	Returns part of a string between specified indexes without changing the original string.	"JavaScript".slice(0, 4); // "Java"
.substring()	Extract Substring	Returns part of a string between specified indexes.	"JavaScript".substring(4, 10); // "Script"
.replace()	Replace Text	Returns a new string with text matching a string or regular expression replaced.	"Hello world".replace("world", "Jennifer");
.replaceAll()	Replace All Matches	Returns a new string with all matching values replaced.	"one one".replaceAll("one", "two");
.trim()	Remove Outer Whitespace	Returns a new string with whitespace removed from both ends.	" hello ".trim(); // "hello"
.repeat()	Repeat String	Returns a new string containing the original string repeated a specified number of times.	"Hi ".repeat(3); // "Hi Hi Hi "
.toUpperCase()	Uppercase Text	Returns a new string with alphabetic characters converted to uppercase.	"hello".toUpperCase(); // "HELLO"
.toLowerCase()	Lowercase Text	Returns a new string with alphabetic characters converted to lowercase.	"HELLO".toLowerCase(); // "hello"
.split()	Split String	Splits a string around a specified separator and returns the parts in an array.	"HTML,CSS,JavaScript".split(",");
.charAt()	Character at Index	Returns the character at a specified zero-based index.	"JavaScript".charAt(0); // "J"

Formatting numbers and performing common rounding, comparison, randomization, and mathematical operations.

Term / Syntax	Name	Description	Example
.toFixed()	Fixed Decimal Places	Formats a number using a specified number of decimal places and returns the result as a string.	(12.5).toFixed(2); // "12.50"
Number.isInteger()	Integer Check	Checks whether a value is a number with no fractional part.	Number.isInteger(42); // true
Math.round()	Round Number	Rounds a number to the nearest integer.	Math.round(4.6); // 5
Math.floor()	Round Down	Rounds a number down to the nearest integer.	Math.floor(4.9); // 4
Math.ceil()	Round Up	Rounds a number up to the nearest integer.	Math.ceil(4.1); // 5
Math.trunc()	Remove Decimal Portion	Returns the integer portion of a number by removing its fractional digits.	Math.trunc(4.9); // 4
Math.abs()	Absolute Value	Returns the absolute value of a number.	Math.abs(-10); // 10
Math.min()	Minimum Value	Returns the smallest number from the provided values.	Math.min(4, 8, 2); // 2
Math.max()	Maximum Value	Returns the largest number from the provided values.	Math.max(4, 8, 2); // 8
Math.random()	Random Number	Returns a pseudorandom number greater than or equal to 0 and less than 1.	Math.random();
Math.floor(Math.random() * max)	Random Integer	Creates a random integer from 0 up to, but not including, a specified maximum.	Math.floor(Math.random() * 10); // 0–9
Math.pow()	Exponent	Raises a number to a specified power.	Math.pow(2, 3); // 8
Math.sqrt()	Square Root	Returns the square root of a number.	Math.sqrt(64); // 8

Creating, reading, updating, formatting, and comparing dates and times.

Term / Syntax	Name	Description	Example
new Date()	Date Object	Creates a Date object representing a specific date and time or the current moment.	const now = new Date();
Date.now()	Current Timestamp	Returns the current timestamp as milliseconds since January 1, 1970 UTC.	const timestamp = Date.now();
.getFullYear()	Year	Returns the four-digit year of a Date.	date.getFullYear();
.getMonth()	Month	Returns the zero-based month of a Date, where January is 0 and December is 11.	date.getMonth();
.getDate()	Day of Month	Returns the day of the month as a number from 1 through 31.	date.getDate();
.getDay()	Day of Week	Returns the zero-based day of the week, where Sunday is 0 and Saturday is 6.	date.getDay();
.getHours()	Hour	Returns the hour of a Date as a number from 0 through 23.	date.getHours();
.getMinutes()	Minutes	Returns the minutes of a Date as a number from 0 through 59.	date.getMinutes();
.getSeconds()	Seconds	Returns the seconds of a Date as a number from 0 through 59.	date.getSeconds();
.getTime()	Date Timestamp	Returns a Date's timestamp as milliseconds since January 1, 1970 UTC.	date.getTime();
< >	Compare Dates	Compares Date objects chronologically to determine whether one occurs before or after another.	startDate < endDate; // true
.setFullYear()	Set Year	Changes the year of a Date and mutates the original Date object.	date.setFullYear(2027);
.setMonth()	Set Month	Changes the zero-based month of a Date and mutates the original Date object.	date.setMonth(5);
.setDate()	Set Day of Month	Changes the day of the month and mutates the original Date object.	date.setDate(15);
.toISOString()	ISO Date String	Returns a Date as a standardized ISO 8601 string in UTC.	date.toISOString();
.toLocaleDateString()	Localized Date	Returns a locale-sensitive string representing the date portion of a Date.	date.toLocaleDateString();
.toLocaleTimeString()	Localized Time	Returns a locale-sensitive string representing the time portion of a Date.	date.toLocaleTimeString();

Common regular expression syntax and methods.

Term / Syntax	Name	Description	Example
/pattern/flags	Regular Expression Literal	Creates a regular expression using literal syntax.	const pattern = /javascript/i;
new RegExp()	Regular Expression Constructor	Creates a regular expression from a string pattern and optional flags.	const pattern = new RegExp("javascript", "i");
.test()	Pattern Check	Checks whether a regular expression matches part of a string.	/javascript/i.test("JavaScript"); // true
.match()	Find Matches	Returns matches between a string and a regular expression.	"JavaScript".match(/script/i);
.replace()	Replace Pattern Match	Returns a new string with text matching a regular expression replaced.	"hello world".replace(/world/i, "Jennifer");
.search()	Find Match Position	Returns the index of the first regular expression match, or -1 if no match is found.	"JavaScript".search(/script/i); // 4
g i m	Common Flags	Changes how a regular expression searches, including global, case-insensitive and multiline matching.	const pattern = /javascript/gi;
\d \w \s	Character Classes	Matches common character groups such as digits, word characters and whitespace.	/\d+/.test("Order 42"); // true
^ $	String Anchors	Matches the beginning or end of a string.	/^Hello/.test("Hello Jennifer"); // true
* + ? { }	Quantifiers	Controls how many times part of a pattern may repeat.	/\d{5}/.test("43016"); // true

Converting between JSON text and JavaScript values.

Term / Syntax	Name	Description	Example
JSON.parse()	Parse JSON	Parses JSON text and returns the corresponding JavaScript value.	const user = JSON.parse(json);
JSON.stringify()	Create JSON	Converts a JavaScript value into a JSON string.	const json = JSON.stringify(user);