JavaScript String Methods

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JavaScript String Methods

2024-03-01 21:37| 来源: 网络整理| 查看: 265

JavaScript String Methods ❮ Previous Next ❯ Basic String Methods

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

String length String charAt() String charCodeAt() String at() String [ ] String slice() String substring() String substr() See Also: String Search Methods String Templates String toUpperCase() String toLowerCase() String concat() String trim() String trimStart() String trimEnd() String padStart() String padEnd() String repeat() String replace() String replaceAll() String split() JavaScript String Length

The length property returns the length of a string:

Example let text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; let length = text.length; Try it Yourself » 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); Try it Yourself » 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); Try it Yourself » JavaScript String at()

ES2022 introduced the string method at():

Examples

Get the third letter of name:

const name = "W3Schools"; let letter = name.at(2); Try it Yourself »

Get the third letter of name:

const name = "W3Schools"; let letter = name[2]; Try it Yourself »

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:

Note

The at() method is a new addition to JavaScript.

It allows the use of negative indexes while charAt() do not.

Now you can use myString.at(-2) instead of charAt(myString.length-2). Browser Support

at() is an ES2022 feature.

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

Chrome 94 Edge 94 Firefox 93 Safari 16.4 Opera 79 Sep 2021 Sep 2021 Oct 2021 Mar 2023 Oct 2021 Property Access [ ] Example let text = "HELLO WORLD"; let char = text[0]; Try it Yourself » Note

Property access might be a little unpredictable:

It makes strings look like arrays (but they are not) If no character is found, [ ] returns undefined, while charAt() returns an empty string. It is read only. str[0] = "A" gives no error (but does not work!) Example let text = "HELLO WORLD"; text[0] = "A"; // Gives no error, but does not work Try it Yourself » 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

Slice out a portion of a string from position 7 to position 13:

let text = "Apple, Banana, Kiwi"; let part = text.slice(7, 13); Try it Yourself » Note

JavaScript counts positions from zero.

First position is 0.

Second position is 1.

Examples

If you omit the second parameter, the method will slice out the rest of the string:

let text = "Apple, Banana, Kiwi"; let part = text.slice(7); Try it Yourself »

If a parameter is negative, the position is counted from the end of the string:

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

This example slices out a portion of a string from position -12 to position -6:

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

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); Try it Yourself »

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); Try it Yourself »

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); Try it Yourself » 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(); Try it Yourself » JavaScript String toLowerCase() Example let text1 = "Hello World!"; // String let text2 = text1.toLowerCase(); // text2 is text1 converted to lower Try it Yourself » JavaScript String concat()

concat() joins two or more strings:

Example let text1 = "Hello"; let text2 = "World"; let text3 = text1.concat(" ", text2); Try it Yourself »

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!"); Note

All string methods return a new string. They don't modify the original string.

Formally said:

Strings are immutable: Strings cannot be changed, only replaced.

JavaScript String trim()

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

Example let text1 = " Hello World! "; let text2 = text1.trim(); Try it Yourself » 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(); Try it Yourself »

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

Chrome 66 Edge 79 Firefox 61 Safari 12 Opera 50 Apr 2018 Jan 2020 Jun 2018 Sep 2018 May 2018 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(); Try it Yourself »

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

Chrome 66 Edge 79 Firefox 61 Safari 12 Opera 50 Apr 2018 Jan 2020 Jun 2018 Sep 2018 May 2018 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

Pad a string with "0" until it reaches the length 4:

let text = "5"; let padded = text.padStart(4,"0"); Try it Yourself »

Pad a string with "x" until it reaches the length 4:

let text = "5"; let padded = text.padStart(4,"x"); Try it Yourself » Note

The padStart() method is a string method.

To pad a number, convert the number to a string first.

See the example below.

Example let numb = 5; let text = numb.toString(); let padded = text.padStart(4,"0"); Try it Yourself » Browser Support

padStart() is an ECMAScript 2017 feature.

ES2017 is supported in all modern browsers since September 2017:

Chrome 58 Edge 15 Firefox 52 Safari 11 Opera 45 Apr 2017 Apr 2017 Mar 2017 Sep 2017 May 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.

Examples let text = "5"; let padded = text.padEnd(4,"0"); Try it Yourself » let text = "5"; let padded = text.padEnd(4,"x"); Try it Yourself » Note

The padEnd() method is a string method.

To pad a number, convert the number to a string first.

See the example below.

Example let numb = 5; let text = numb.toString(); let padded = text.padEnd(4,"0"); Try it Yourself » Browser Support

padEnd() is an ECMAScript 2017 feature.

ES2017 is supported in all modern browsers since September 2017:

Chrome 58 Edge 15 Firefox 52 Safari 11 Opera 45 Apr 2017 Apr 2017 Mar 2017 Sep 2017 May 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.

Examples

Create copies of a text:

let text = "Hello world!"; let result = text.repeat(2); Try it Yourself » let text = "Hello world!"; let result = text.repeat(4); Try it Yourself » Syntax string.repeat(count) Parameters Parameter Description countRequired. The number of copies wanted. Return Value Type Description StringA new string containing the copies. Browser Support

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

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

Chrome 51 Edge 15 Firefox 54 Safari 10 Opera 38 May 2016 Apr 2017 Jun 2017 Sep 2016 Jun 2016

repeat() is not supported in Internet Explorer.

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", "W3Schools"); Try it Yourself » Note

The replace() method does not change the string it is called on.

The replace() method returns a new string.

The replace() method replaces only the first match

If you want to replace all matches, use a regular expression with the /g flag set. See examples below.

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

Example let text = "Please visit Microsoft and Microsoft!"; let newText = text.replace("Microsoft", "W3Schools");

Try it Yourself »

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", "W3Schools");

Try it Yourself »

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, "W3Schools");

Try it Yourself »

Note

Regular expressions are written without quotes.

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, "W3Schools");

Try it Yourself »

Note

You will learn a lot more about regular expressions in the chapter JavaScript Regular Expressions.

JavaScript String ReplaceAll()

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

Example text = text.replaceAll("Cats","Dogs"); text = text.replaceAll("cats","dogs"); Try it Yourself »

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"); Try it Yourself » Note

replaceAll() is an ES2021 feature.

replaceAll() does not work in Internet Explorer.

Converting a String to an Array

If you want to work with a string as an array, you can convert it to an array.

JavaScript String split()

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

Example text.split(",") // Split on commas text.split(" ") // Split on spaces text.split("|") // Split on pipe Try it Yourself »

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:

Example text.split("") Try it Yourself » Complete String Reference

For a complete String reference, go to our:

Complete JavaScript String Reference.

The reference contains descriptions and examples of all string properties and methods.

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