JavaScript Reference: String

JavaScript strings are immutable sequences of UTF-16 code units.

String indexes and length count UTF-16 code units, not necessarily user-perceived characters. The MDN String reference explains the Unicode details.

Call String() without new to convert a value to a string:

String(42) //'42'

Static methods

The String object has three static methods.

String.fromCharCode() creates a string from UTF-16 code units:

String.fromCharCode(70, 108, 97, 118, 105, 111) //'Flavio'

String.fromCodePoint() creates a string from Unicode code points:

String.fromCodePoint(70, 108, 97, 118, 105, 111) //'Flavio'

This matters for characters outside the basic multilingual plane:

String.fromCodePoint(0x1F436) //'🐶'

String.raw() returns the raw text of a tagged template literal:

String.raw`line 1\nline 2` //'line 1\\nline 2'

All other methods below are instance methods. JavaScript temporarily wraps a string primitive so you can call them directly.

Instance methods

A string offers many methods. The most commonly used are:

• at(i)
• charAt(i)
• charCodeAt(i)
• codePointAt(i)
• concat(str)
• endsWith(str)
• includes(str)
• indexOf(str)
• lastIndexOf(str)
• localeCompare()
• match(regex)
• matchAll(regex)
• normalize()
• padEnd()
• padStart()
• repeat()
• replace(str1, str2)
• replaceAll(str1, str2)
• search(regexp)
• slice(begin, end)
• split(separator)
• startsWith(str)
• substring()
• toLocaleLowerCase()
• toLocaleUpperCase()
• toLowerCase()
• toString()
• toUpperCase()
• trim()
• trimEnd()
• trimStart()
• valueOf()
• isWellFormed()
• toWellFormed()

Strings are immutable. These methods return new strings instead of changing the original value:

const name = 'Flavio'
const upper = name.toUpperCase()

name //'Flavio'
upper //'FLAVIO'

Avoid the old HTML wrapper methods such as bold() and fontcolor(). They are deprecated. Use HTML and CSS instead.

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