- JavaScript String Methods
- JavaScript String Length
- Example
- Extracting String Parts
- JavaScript String slice()
- Example
- Note
- Examples
- JavaScript String substring()
- Example
- JavaScript String substr()
- Example
- Example
- Example
- Replacing String Content
- Example
- Note
- Example
- Example
- Example
- Note
- Example
- Note
- JavaScript String ReplaceAll()
- Example
- Example
- Note
- Converting to Upper and Lower Case
- JavaScript String toUpperCase()
- Example
- JavaScript String toLowerCase()
- Example
- JavaScript String concat()
- Example
- Example
- Note
- JavaScript String trim()
- Example
- JavaScript String trimStart()
- Example
- JavaScript String trimEnd()
- Example
- JavaScript String Padding
- JavaScript String padStart()
- Examples
- Note
- Example
- Browser Support
- JavaScript String padEnd()
- Examples
- Note
- Example
- Browser Support
- Extracting String Characters
- JavaScript String charAt()
- Example
- JavaScript String charCodeAt()
- Example
- Property Access
- Example
- Note
- Example
- Converting a String to an Array
- JavaScript String split()
- Example
- Example
- Complete String Reference
- String.prototype.substring()
- Try it
- Syntax
- Parameters
- Return value
- Description
- Examples
- Using substring()
- Using substring() with length property
- The difference between substring() and substr()
- Differences between substring() and slice()
- Replacing a substring within a string
- Specifications
- Browser compatibility
- See also
- Found a content problem with this page?
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JavaScript String Methods
String search methods are covered in the next chapter.
JavaScript String Length
The length property returns the length of a string:
Example
Extracting String Parts
There are 3 methods for extracting a part of a string:
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:
Note
JavaScript counts positions from zero.
Examples
If you omit the second parameter, the method will slice out the rest of the string:
If a parameter is negative, the position is counted from the end of the string:
This example slices out a portion of a string from position -12 to position -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() .
Example
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
If you omit the second parameter, substr() will slice out the rest of the string.
Example
If the first parameter is negative, the position counts from the end of the string.
Example
Replacing String Content
The replace() method replaces a specified value with another value in a string:
Example
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»);
By default, the replace() method is case sensitive. Writing MICROSOFT (with upper-case) will not work:
Example
To replace case insensitive, use a regular expression with an /i flag (insensitive):
Example
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»);
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
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
Note
replaceAll() is an ES2021 feature.
replaceAll() does not work in Internet Explorer.
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
JavaScript String toLowerCase()
Example
let text1 = «Hello World!»; // String
let text2 = text1.toLowerCase(); // text2 is text1 converted to lower
JavaScript String concat()
concat() joins two or more strings:
Example
The concat() method can be used instead of the plus operator. These two lines do the same:
Example
Note
All string methods return a new string. They don’t modify the original string.
Strings are immutable: Strings cannot be changed, only replaced.
JavaScript String trim()
The trim() method removes whitespace from both sides of a string:
Example
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
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.
Example
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.
Examples
Pad a string with «0» until it reaches the length 4:
Pad a string with «x» until it reaches the length 4:
Note
The padStart() method is a string method.
To pad a number, convert the number to a string first.
Example
Browser Support
It is supported in all modern browsers:
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
Note
The padEnd() method is a string method.
To pad a number, convert the number to a string first.
Example
Browser Support
It is supported in all modern browsers:
padEnd() is not supported in Internet Explorer.
Extracting String Characters
There are 3 methods for extracting string characters:
JavaScript String charAt()
The charAt() method returns the character at a specified index (position) in a string:
Example
JavaScript String charCodeAt()
The charCodeAt() method returns the unicode of the character at a specified index in a string:
The method returns a UTF-16 code (an integer between 0 and 65535).
Example
Property Access
ECMAScript 5 (2009) allows property access [ ] on strings:
Example
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
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
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
Complete String Reference
For a complete String reference, go to our:
The reference contains descriptions and examples of all string properties and methods.
String.prototype.substring()
The substring() method returns the part of the string from the start index up to and excluding the end index, or to the end of the string if no end index is supplied.
Try it
Syntax
substring(indexStart) substring(indexStart, indexEnd)
Parameters
The index of the first character to include in the returned substring.
The index of the first character to exclude from the returned substring.
Return value
A new string containing the specified part of the given string.
Description
substring() extracts characters from indexStart up to but not including indexEnd . In particular:
- If indexEnd is omitted, substring() extracts characters to the end of the string.
- If indexStart is equal to indexEnd , substring() returns an empty string.
- If indexStart is greater than indexEnd , then the effect of substring() is as if the two arguments were swapped; see example below.
Any argument value that is less than 0 or greater than str.length is treated as if it were 0 and str.length , respectively.
Any argument value that is NaN is treated as if it were 0 .
Examples
Using substring()
The following example uses substring() to display characters from the string ‘Mozilla’ :
const anyString = "Mozilla"; console.log(anyString.substring(0, 1)); // 'M' console.log(anyString.substring(1, 0)); // 'M' console.log(anyString.substring(0, 6)); // 'Mozill' console.log(anyString.substring(4)); // 'lla' console.log(anyString.substring(4, 7)); // 'lla' console.log(anyString.substring(7, 4)); // 'lla' console.log(anyString.substring(0, 7)); // 'Mozilla' console.log(anyString.substring(0, 10)); // 'Mozilla'
Using substring() with length property
The following example uses the substring() method and length property to extract the last characters of a particular string. This method may be easier to remember, given that you don’t need to know the starting and ending indices as you would in the above examples.
const text = "Mozilla"; // Takes 4 last characters of string console.log(text.substring(text.length - 4)); // prints "illa" // Takes 5 last characters of string console.log(text.substring(text.length - 5)); // prints "zilla"
The difference between substring() and substr()
There are subtle differences between the substring() and substr() methods, so you should be careful not to get them confused.
- The two parameters of substr() are start and length , while for substring() , they are start and end .
- substr() ‘s start index will wrap to the end of the string if it is negative, while substring() will clamp it to 0 .
- Negative lengths in substr() are treated as zero, while substring() will swap the two indexes if end is less than start .
Furthermore, substr() is considered a legacy feature in ECMAScript, so it is best to avoid using it if possible.
const text = "Mozilla"; console.log(text.substring(2, 5)); // "zil" console.log(text.substr(2, 3)); // "zil"
Differences between substring() and slice()
The substring() and slice() methods are almost identical, but there are a couple of subtle differences between the two, especially in the way negative arguments are dealt with.
The substring() method swaps its two arguments if indexStart is greater than indexEnd , meaning that a string is still returned. The slice() method returns an empty string if this is the case.
const text = "Mozilla"; console.log(text.substring(5, 2)); // "zil" console.log(text.slice(5, 2)); // ""
If either or both of the arguments are negative or NaN , the substring() method treats them as if they were 0 .
.log(text.substring(-5, 2)); // "Mo" console.log(text.substring(-5, -2)); // ""
slice() also treats NaN arguments as 0 , but when it is given negative values it counts backwards from the end of the string to find the indexes.
.log(text.slice(-5, 2)); // "" console.log(text.slice(-5, -2)); // "zil"
See the slice() page for more examples with negative numbers.
Replacing a substring within a string
The following example replaces a substring within a string. It will replace both individual characters and substrings. The function call at the end of the example changes the string Brave New World to Brave New Web .
// Replaces oldS with newS in the string fullS function replaceString(oldS, newS, fullS) for (let i = 0; i fullS.length; ++i) if (fullS.substring(i, i + oldS.length) === oldS) fullS = fullS.substring(0, i) + newS + fullS.substring(i + oldS.length, fullS.length); > > return fullS; > replaceString("World", "Web", "Brave New World");
Note that this can result in an infinite loop if oldS is itself a substring of newS — for example, if you attempted to replace ‘ World ‘ with ‘ OtherWorld ‘ here.
A better method for replacing strings is as follows:
function replaceString(oldS, newS, fullS) return fullS.split(oldS).join(newS); >
The code above serves as an example for substring operations. If you need to replace substrings, most of the time you will want to use String.prototype.replace() .
Specifications
Browser compatibility
BCD tables only load in the browser
See also
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This page was last modified on Feb 21, 2023 by MDN contributors.
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