JavaScript String Methods

JavaScript String Length

The length property returns the length of a string:

let text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
let length = text.length;

Extracting String Characters

There are 4 methods for extracting string characters:

• The at(position) Method
• The charAt(position) Method
• The charCodeAt(position) Method
• Using property access [] like in arrays

JavaScript String charAt()

The charAt() method returns the character at a specified index (position) in a string:

let text = "HELLO WORLD";
let char = text.charAt(0);

JavaScript String charCodeAt()

The charCodeAt() method returns the code of the character at a specified index in a string:

The method returns a UTF-16 code (an integer between 0 and 65535).

let text = "HELLO WORLD";
let char = text.charCodeAt(0);

JavaScript String at()

ES2022 introduced the string method at():

const name = "ScoolioAcademy";
let letter = name.at(2);

const name = "ScoolioAcademy";
let letter = name[2];

The at() method returns the character at a specified index (position) in a string.

The at() method is supported in all modern browsers since March 2022:

Browser Support

at() is an ES2022 feature.

JavaScript 2022 (ES2022) is supported in all modern browsers since March 2023:

Property Access [ ]

let text = "HELLO WORLD";
let char = text[0];

let text = "HELLO WORLD";
text[0] = "A";    // Gives no error, but does not work

Extracting String Parts

There are 3 methods for extracting a part of a string:

• slice(start, end)
• substring(start, end)
• substr(start, length)

JavaScript String slice()

slice() extracts a part of a string and returns the extracted part in a new string.

The method takes 2 parameters: start position, and end position (end not included).

let text = "Apple, Banana, Kiwi";
let part = text.slice(7, 13);

let text = "Apple, Banana, Kiwi";
let part = text.slice(7);

let text = "Apple, Banana, Kiwi";
let part = text.slice(-12);

let text = "Apple, Banana, Kiwi";
let part = text.slice(-12, -6);

JavaScript String substring()

substring() is similar to slice().

The difference is that start and end values less than 0 are treated as 0 in substring().

let str = "Apple, Banana, Kiwi";
let part = str.substring(7, 13);

If you omit the second parameter, substring() will slice out the rest of the string.

JavaScript String substr()

substr() is similar to slice().

The difference is that the second parameter specifies the length of the extracted part.

let str = "Apple, Banana, Kiwi";
let part = str.substr(7, 6);

If you omit the second parameter, substr() will slice out the rest of the string.

let str = "Apple, Banana, Kiwi";
let part = str.substr(7);

If the first parameter is negative, the position counts from the end of the string.

let str = "Apple, Banana, Kiwi";
let part = str.substr(-4);

Converting to Upper and Lower Case

A string is converted to upper case with toUpperCase():

A string is converted to lower case with toLowerCase():

JavaScript String toUpperCase()

let text1 = "Hello World!";
let text2 = text1.toUpperCase();

JavaScript String toLowerCase()

let text1 = "Hello World!";       // String
let text2 = text1.toLowerCase();  // text2 is text1 converted to lower

JavaScript String concat()

concat() joins two or more strings:

let text1 = "Hello";
let text2 = "World";
let text3 = text1.concat(" ", text2);

The concat() method can be used instead of the plus operator. These two lines do the same:

text = "Hello" + " " + "World!";
text = "Hello".concat(" ", "World!");

JavaScript String trim()

The trim() method removes whitespace from both sides of a string:

let text1 = "      Hello World!      ";
let text2 = text1.trim();

JavaScript String trimStart()

ECMAScript 2019 added the String method trimStart() to JavaScript.

The trimStart() method works like trim(), but removes whitespace only from the start of a string.

let text1 = "     Hello World!     ";
let text2 = text1.trimStart();

JavaScript String trimStart() is supported in all modern browsers since January 2020:

JavaScript String trimEnd()

ECMAScript 2019 added the string method trimEnd() to JavaScript.

The trimEnd() method works like trim(), but removes whitespace only from the end of a string.

let text1 = "     Hello World!     ";
let text2 = text1.trimEnd();

JavaScript String trimEnd() is supported in all modern browsers since January 2020:

JavaScript String Padding

ECMAScript 2017 added two new string methods to JavaScript: padStart() and padEnd() to support padding at the beginning and at the end of a string.

JavaScript String padStart()

The padStart() method pads a string from the start.

It pads a string with another string (multiple times) until it reaches a given length.

let text = "5";
let padded = text.padStart(4,"0");

let text = "5";
let padded = text.padStart(4,"x");

let numb = 5;
let text = numb.toString();
let padded = text.padStart(4,"0");

Browser Support

padStart() is an ECMAScript 2017 feature.

ES2017 is supported in all modern browsers since September 2017:

padStart() is not supported in Internet Explorer.

JavaScript String padEnd()

The padEnd() method pads a string from the end.

It pads a string with another string (multiple times) until it reaches a given length.

let text = "5";
let padded = text.padEnd(4,"0");

let text = "5";
let padded = text.padEnd(4,"x");

let numb = 5;
let text = numb.toString();
let padded = text.padEnd(4,"0");

Browser Support

padEnd() is an ECMAScript 2017 feature.

ES2017 is supported in all modern browsers since September 2017:

padEnd() is not supported in Internet Explorer.

JavaScript String repeat()

The repeat() method returns a string with a number of copies of a string.

The repeat() method returns a new string.

The repeat() method does not change the original string.

let text = "Hello world!";
let result = text.repeat(2);

let text = "Hello world!";
let result = text.repeat(4);

Syntax

Parameters

Return Value

Browser Support

repeat() is an ES6 feature (JavaScript 2015).

ES6 is fully supported in all modern browsers since June 2017:

repeat() is not supported in Internet Explorer.

Replacing String Content

The replace() method replaces a specified value with another value in a string:

let text = "Please visit Google!";
let newText = text.replace("Google", "Scoolio");

By default, the replace() method replaces only the first match:

let text = "Please visit Google and Google!";
let newText = text.replace("Google", "Scoolio");

By default, the replace() method is case sensitive. Writing MICROSOFT (with upper-case) will not work:

let text = "Please visit Google!";
let newText = text.replace("GOOGLE", "Scoolio");

To replace case insensitive, use a regular expression with an /i flag (insensitive):

let text = "Please visit Google!";
let newText = text.replace(/GOOGLE/i, "Scoolio");

To replace all matches, use a regular expression with a /g flag (global match):

let text = "Please visit Google and Google!";
let newText = text.replace(/Google/g, "Scoolio");

JavaScript String ReplaceAll()

In 2021, JavaScript introduced the string method replaceAll():

text = text.replaceAll("Cats","Dogs");
text = text.replaceAll("cats","dogs");

The replaceAll() method allows you to specify a regular expression instead of a string to be replaced.

If the parameter is a regular expression, the global flag (g) must be set, otherwise a TypeError is thrown.

text = text.replaceAll(/Cats/g,"Dogs");
text = text.replaceAll(/cats/g,"dogs");

Converting a String to an Array

JavaScript String split()

A string can be converted to an array with the split() method:

text.split(",")    // Split on commas
text.split(" ")    // Split on spaces
text.split("|")    // Split on pipe

If the separator is omitted, the returned array will contain the whole string in index [0].

If the separator is "", the returned array will be an array of single characters:

text.split("")

let text = "Please locate where 'locate' occurs!";
let index = text.indexOf("locate");

let text = "Please locate where 'locate' occurs!";
let index = text.lastIndexOf("locate");

let text = "Please locate where 'locate' occurs!";
let index = text.lastIndexOf("John");

let text = "Please locate where 'locate' occurs!";
let index = text.indexOf("locate", 15);

let text = "Please locate where 'locate' occurs!";
text.lastIndexOf("locate", 15);

let text = "Please locate where 'locate' occurs!";
text.search("locate");

let text = "Please locate where 'locate' occurs!";
text.search(/locate/);

let text = "The rain in SPAIN stays mainly in the plain";
text.match("ain");

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/);

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/g);

let text = "The rain in SPAIN stays mainly in the plain";
text.match(/ain/gi);

const iterator = text.matchAll("Cats");

const iterator = text.matchAll(/Cats/g);

const iterator = text.matchAll(/Cats/gi);

let text = "Hello world, welcome to the universe.";
text.includes("world");

let text = "Hello world, welcome to the universe.";
text.includes("world", 12);

let text = "Hello world, welcome to the universe.";
text.startsWith("Hello");

let text = "Hello world, welcome to the universe.";
text.startsWith("world")

let text = "Hello world, welcome to the universe.";
text.startsWith("world", 5)

let text = "Hello world, welcome to the universe.";
text.startsWith("world", 6)

let text = "John Doe";
text.endsWith("Doe");

let text = "Hello world, welcome to the universe.";
text.endsWith("world", 11);