JavaScript String Methods

Guest · Post by **Guest** » Fri Oct 27, 2023 9:07 am

JavaScript String Methods

String length
String slice()
String substring()
String substr()
String replace()
String replaceAll()
String toUpperCase()
String toLowerCase()
String concat()

String trim()
String trimStart()
String trimEnd()
String padStart()
String padEnd()
String charAt()
String charCodeAt()
String split()

Note
String search methods are covered in the next chapter.

JavaScript String Length
The length property returns the length of a string:

Example

let text = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
let length = text.length;

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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);

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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);

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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);

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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);

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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);

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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);

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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);

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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);

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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");

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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");

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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");

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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");

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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");

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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");

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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");

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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

let text1 = "Hello World!";
let text2 = text1.toUpperCase();

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JavaScript String toLowerCase()

Example

let text1 = "Hello World!";       // String
let text2 = text1.toLowerCase();  // text2 is text1
converted to lower

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JavaScript String concat()
concat() joins two or more strings:

Example

let text1 = "Hello";
let text2 = "World";
let text3 = text1.concat(" ", text2);

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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();

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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();

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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();

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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");

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

let text = "5";
let padded = text.padStart(4,"x");

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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");

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Browser Support
padStart() is an ECMAScript 2017 feature.
It is supported in all modern browsers:

Chrome
Edge
Firefox
Safari
Opera

Yes
Yes
Yes
Yes
Yes

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");

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let text = "5";
let padded = text.padEnd(4,"x");

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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");

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Browser Support
padEnd() is an ECMAScript 2017 feature.
It is supported in all modern browsers:

Chrome
Edge
Firefox
Safari
Opera

Yes
Yes
Yes
Yes
Yes

padEnd() is not supported in Internet Explorer.

Extracting String Characters
There are 3 methods for extracting string characters:

charAt(position)
charCodeAt(position)
Property access [ ]

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);

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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

let text = "HELLO WORLD";
let char = text.charCodeAt(0);

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Property Access
ECMAScript 5 (2009) allows property access [ ] on strings:

Example

let text = "HELLO WORLD";
let char = text[0];

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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

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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

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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("")

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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.

Test Yourself With Exercises

Exercise:
Convert the text into an UPPERCASE text:

let txt = "Hello World!";
txt = txt.;

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Start the Exercise

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Reference: https://www.w3schools.com/js/js_string_methods.asp