JavaScript String Methods
Basic String Methods
Javascript strings are primitive and immutable: All string methods produce a new string without altering the original string.
String charAt()
String charCodeAt()
String codePointAt()
String concat()
String at()
String [ ]
String slice()
String substring()
String substr()
String toUpperCase()
String toLowerCase()
String isWellFormed()
String toWellFormed()
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:
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:
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).
JavaScript codePointAt()
Examples
Get code point value at the first position in a string:
let code = text.codePointAt(0);
JavaScript String at()
ES2022 introduced the string method at():
Examples
Get the third letter of name:
let letter = name.at(2);
Get the third letter of name:
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:
Note
The at() method is a new addition to JavaScript.
It allows the use of negative indexes while charAt() do not.
myString.at(-2) instead of
charAt(myString.length-2).
Browser Support
at() is an ES2022 feature.
JavaScript 2022 is supported in all modern browsers since March 2022:
| Chrome 92 |
Edge 92 |
Firefox 90 |
Safari 15.4 |
Opera 78 |
| Apr 2021 | Jul 2021 | Jul 2021 | Mar 2022 | Aug 2021 |
Property Access [ ]
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
text[0] = "A"; // Gives no error, but does not work
JavaScript String concat()
concat() joins two or more strings:
Example
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".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.
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 part = text.slice(7, 13);
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 part = text.slice(7);
If a parameter is negative, the position is counted from the end of the string:
let part = text.slice(-12);
This example slices out a portion of a string from position -12 to position -6:
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().
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.
Warning
The substr() method is removed (deprecated) in the latest JavaScript standard.
Use substring() or slice() instead.
If you omit the second parameter, substr() will slice out the rest of the
string.
If the first parameter is negative, the position counts from the end of the string.
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()
JavaScript String toLowerCase()
Example
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 result = text.isWellFormed();
let result = text.isWellFormed();
Lone Surrogates
A lone surrogate is a Unicode surrogate code point that is not part of a valid surrogate pair used to represent characters in UTF-16 encoding.
JavaScript String toWellFormed()
The String method toWellFormed()
returns a new string where all "lone surrogates" are replaced with the Unicode replacement character (U+FFFD).
JavaScript String trim()
The trim() method removes whitespace from both sides of a string:
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.
Browser Support
trimStart() is an ECMAScript 2019 feature.
ES2019 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.
Browser Support
trimEnd() is an ECMAScript 2019 feature.
ES2019 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 padded = text.padStart(4,"0");
Pad a string with "x" until it reaches the length 4:
let padded = text.padStart(4,"x");
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 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:
| Chrome 58 |
Edge 15 |
Firefox 52 |
Safari 11 |
Opera 45 |
| Apr 2017 | Apr 2017 | Mar 2017 | Sep 2017 | May 2017 |
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 padded = text.padEnd(4,"0");
let padded = text.padEnd(4,"x");
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 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:
| Chrome 58 |
Edge 15 |
Firefox 52 |
Safari 11 |
Opera 45 |
| Apr 2017 | Apr 2017 | Mar 2017 | Sep 2017 | May 2017 |
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 result = text.repeat(2);
let result = text.repeat(4);
Syntax
Parameters
The number of copies wanted.
Return Value
Browser Support
repeat() is an ES6 feature.
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 |
Replacing String Content
The replace() method replaces a specified value with another
value in a string:
Example
let newText = text.replace("Microsoft", "W3Schools");
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 newText = text.replace("Microsoft", "W3Schools");
By default, the replace() method is case sensitive. Writing MICROSOFT (with
upper-case) will not work:
Example
let newText = text.replace("MICROSOFT", "W3Schools");
To replace case insensitive, use a regular expression with an /i flag (insensitive):
Example
let newText = text.replace(/MICROSOFT/i, "W3Schools");
Note
Regular expressions are written without quotes.
To replace all matches, use a regular expression with a /g flag (global match):
Example
let newText = text.replace(/Microsoft/g, "W3Schools");
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");
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");
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 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:
Complete JavaScript Reference
For a complete reference to all JavaScript properties and methods, with full descriptions and many examples, go to:
W3Schools' Full JavaScript Reference.
The reference inludes all JavaScript updates from 1999 to 2025.