Javascript start with substring

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.

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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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