JavaScript String Methods

Basic String Methods

Javascript strings are primitive and immutable: All string methods produce a new string without altering the original string.

JavaScript String Length

The length property returns the length of a string:

Example

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:

Example

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).

Example

let text = "HELLO WORLD";

let char = text.charCodeAt(0);

JavaScript codePointAt()

Examples

let text = "HELLO WORLD";

let code = text.codePointAt(0);

JavaScript String at()

ES2022 introduced the string method at():

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:

Examples

const name = "EA Academy";

let letter = name.at(2);

Examples

const name = "EA Academy";

let letter = name.at(-5);

Browser Support

at() is an ECMAScript 2022 feature.

JavaScript 2022 is supported in all modern browsers since March 2022:

Property Access [ ]

Example

let text = "HELLO WORLD";

let char = text[0];

Example (Sloppy Mode)

let text = "HELLO WORLD";

// Try to change the first letter to "A"

try {

  text[0] = "A";

} catch(err) {

  text = err.message

}

Example (Strict Mode)

"using strict";

let text = "HELLO WORLD";

// Try to change the first letter to "A"

try {

 text[0] = "A";

} catch(err) {

 text = err.message

}

JavaScript String concat()

concat() joins two or more strings:

Example

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:

Example

text = "Hello" + " " + "World!";

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

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).

Example

let text = "Apple, Banana, Kiwi";

let part = text.slice(7, 13);

Examples

let text = "Apple, Banana, Kiwi";

let part = text.slice(7);

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().

Example

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.

Example

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.

Example

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.

Example

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()

Example

let text1 = "Hello World!";

let text2 = text1.toUpperCase();

JavaScript String toLowerCase()

Example

let text1 = "Hello World!";       // String

let text2 = text1.toLowerCase();  // text2 is text1
converted to lower

JavaScript String isWellFormed()

The isWellFormed() method returns true if a string is well formed.

Otherwise it returns false.

A string is not well formed if it contains lone surrogates.

Examples

let text = "Hello world!";

let result = text.isWellFormed();

JavaScript String toWellFormed()

The String method toWellFormed() returns a new string where all "lone surrogates" are replaced with the Unicode replacement character (U+FFFD). ### Examples ``javascript let text = "Hello World \uD800"; let result = text.toWellFormed(); ` --- ## JavaScript String trim() The trim()` method removes whitespace from both sides of a string:

Example

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.

Example

let text1 = "     Hello World!     ";

let text2 = text1.trimStart();

Browser Support

trimStart() is an ECMAScript 2019 feature.

ES2019 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.

Example

let text1 = "     Hello World!     ";

let text2 = text1.trimEnd();

Browser Support

trimEnd() is an ECMAScript 2019 feature.

ES2019 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.

Examples

let text = "5";

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

Example

let numb = 5;

let text = numb.toString();

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

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.

Examples

let text = "5";

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

Example

let numb = 5;

let text = numb.toString();

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

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.

Examples

let text = "Hello world!";

let result = text.repeat(2);

Syntax

string.repeat(count)

Parameters

Return Value

Replacing String Content

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

Example

let text = "Please visit Microsoft!";

let newText = text.replace("Microsoft", "EA Academy");

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

Example

let text = "Please visit Microsoft and Microsoft!";

let newText = text.replace("Microsoft", "EA Academy");

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

Example

let text = "Please visit Microsoft!";

let newText = text.replace("MICROSOFT", "EA Academy");

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

Example

let text = "Please visit Microsoft!";

let newText = text.replace(/MICROSOFT/i, "EA Academy");

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

Example

let text = "Please visit Microsoft and Microsoft!";

let newText = text.replace(/Microsoft/g, "EA Academy");

JavaScript String ReplaceAll()

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

Example

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.

Example

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:

Syntax

text.split("")     // Split on characters

text.split(",")    // Split on commas

text.split(" ")    // Split on spaces

text.split("|")    // Split on pipe

Examples

let text = "Hi fox!";

const myArr = text.split("");

Using split("") Can be Unsafe

Using split("") is unsafe for strings containing emojis or complex characters.

The method splits by UTF-16 code units and will break surrogate pairs.

split("") is always unsafe for emojis. It will slice right through them and create broken, corrupt code fragments.

split(" ") is usually safe for words, even if they have emojis inside them, as long as the emoji is not glued right next to a space you are splitting on.

Summary of Options:

• text.split("") is most unsafe It breaks up 4-byte emojis (like 💩 becomes ['\uD83D', '\uDCA9']).
• Spread [...text] is partially safe: It works for simple emojis like 💩 or 🔥, but destroys complex emojis like 👨‍👩‍👧‍👦, 🧑‍⚕️ (doctor), or flags.
• Intl.Segmenter is 100% Safe: It handles every emoji, accent, and complex characters.

Examples

let text = "👨‍👩‍👧‍👦";

const myArr = text.split("");