JavaScript String Methods

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String Methods And Properties

Primitive values, like "John Doe", cannot have properties or methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.

String Length

The length property returns the length of a string:

Example

var txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
var sln = txt.length;

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Finding a String in a String

The indexOf() method returns the index of (the position of) the first occurrence of a specified text in a string:

Example

var str = "Please locate where 'locate' occurs!";
var pos = str.indexOf("locate");

JavaScript counts positions from zero.
0 is the first position in a string, 1 is the second, 2 is the third ...

The lastIndexOf() method returns the index of the last occurrence of a specified text in a string:

Example

var str = "Please locate where 'locate' occurs!";
var pos = str.lastIndexOf("locate");

Both indexOf(), and lastIndexOf() return -1 if the text is not found.

Example

var str = "Please locate where 'locate' occurs!";
var pos = str.lastIndexOf("John");

Both methods accept a second parameter as the starting position for the search:

Example

var str = "Please locate where 'locate' occurs!";
var pos = str.indexOf("locate", 15);

The lastIndexOf() methods searches backwards (from the end to the beginning), meaning: if the second parameter is 15, the search starts at position 15, and searches to the beginning of the string.

Example

var str = "Please locate where 'locate' occurs!";
var pos = str.lastIndexOf("locate", 15);

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Searching For A String In A String

The search() method searches a string for a specified value and returns the position of the match:

Example

var str = "Please locate where 'locate' occurs!";
var pos = str.search("locate");

Did You Notice?

The two methods, indexOf() and search(), are equal?

They accept the same arguments (parameters), and return the same value?

The two methods are NOT equal. These are the differences:

The search() method cannot take a second start position argument.
The indexOf() method cannot take powerful search values (regular expressions).

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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)

The slice() Method

slice() extracts a part of a string and returns the extracted part in a new string.

The method takes 2 parameters: the start position, and the end position (end not included).

This example slices out a portion of a string from position 7 to position 12 (13-1):

Example

var str = "Apple, Banana, Kiwi";
var res = str.slice(7, 13);

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The result of res will be:

Banana

Remember: JavaScript counts positions from zero. First position is 0.

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:

Example

var str = "Apple, Banana, Kiwi";
var res = str.slice(-12, -6);

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The result of res will be:

Banana

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

Example

var res = str.slice(7);

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or, counting from the end:

Example

var res = str.slice(-12);

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Negative positions do not work in Internet Explorer 8 and earlier.

The substring() Method

substring() is similar to slice().

The difference is that substring() cannot accept negative indexes.

Example

var str = "Apple, Banana, Kiwi";
var res = str.substring(7, 13);

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The result of res will be:

Banana

If you omit the second parameter, substring() will slice out the rest of the string.

The substr() Method

substr() is similar to slice().

The difference is that the second parameter specifies the length of the extracted part.

Example

var str = "Apple, Banana, Kiwi";
var res = str.substr(7, 6);

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The result of res will be:

Banana

If you omit the second parameter, substr() will slice out the rest of the string.

Example

var str = "Apple, Banana, Kiwi";
var res = str.substr(7);

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The result of res will be:

Banana, Kiwi

If the first parameter is negative, the position counts from the end of the string.

Example

var str = "Apple, Banana, Kiwi";
var res = str.substr(-4);

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The result of res will be:

Kiwi

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Replacing String Content

The replace() method replaces a specified value with another value in a string:

Example

str = "Please visit Microsoft!";
var n = str.replace("Microsoft", "Mytat");

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The replace() method does not change the string it is called on. It returns a new string.

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

Example

str = "Please visit Microsoft and Microsoft!";
var n = str.replace("Microsoft", "Mytat");

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By default, the replace() method is case sensitive. Writing MICROSOFT (with upper-case) will not work:

Example

str = "Please visit Microsoft!";
var n = str.replace("MICROSOFT", "Mytat");

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To replace case insensitive, use a regular expression with an /i flag (insensitive):

Example

str = "Please visit Microsoft!";
var n = str.replace(/MICROSOFT/i, "Mytat");

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Note that regular expressions are written without quotes.

To replace all matches, use a regular expression with a /g flag (global match):

Example

str = "Please visit Microsoft and Microsoft!";
var n = str.replace(/Microsoft/g, "Mytat");

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Converting To Upper And Lower Case

A string is converted to upper case with toUpperCase():

Example

var text1 = "Hello World!"; // String
var text2 = text1.toUpperCase(); // text2 is text1 converted to upper

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A string is converted to lower case with toLowerCase():

Example

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

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The Concat() Method

concat() joins two or more strings:

Example

var text1 = "Hello";
var text2 = "World";
var 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

var text = "Hello" + " " + "World!";
var text = "Hello".concat(" ", "World!");

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.

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String.trim()

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

Example

var str = " Hello World! ";
alert(str.trim());

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The trim() method is not supported in Internet Explorer 8 or lower.

If you need to support IE 8, you can use replace() with a regular expression instead:

Example

var str = " Hello World! ";
alert(str.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g, ''));

You can also use the replace solution above to add a trim function to the JavaScript String.prototype:

Example

if (!String.prototype.trim) {
  String.prototype.trim = function () {
   return this.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g, '');
};
}
var str = "       Hello World!        ";
alert(str.trim());

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JavaScript String Padding

ECMAScript 2017 added two String methods: padStart and padEnd to support padding at the beginning and at the end of a string.

Example

let str = "5";
str = str.padStart(4,0);
// result is 0005

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Example

let str = "5";
str = str.padEnd(4,0);
// result is 5000

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String Padding is not supported in Internet Explorer.

Firefox and Safari were the first browsers with support for JavaScript string padding:

Chrome 57	Edge 15	Firefox 48	Safari 10	Opera 44
Mar 2017	Apr 2017	Aug 2016	Sep 2016	Mar 2017

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Converting A String To An Array

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

Example

var txt = "a,b,c,d,e";   // String
txt.split(",");          // Split on commas
txt.split(" ");          // Split on spaces
txt.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

var txt = "Hello"; // String
txt.split(""); // Split in characters

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How To Recognize An Array

A common question is: How do I know if a variable is an array?

The problem is that the JavaScript operator typeof returns "object":

var fruits = ["Banana", "Orange", "Apple", "Mango"];

typeof fruits; // returns object

The typeof operator returns object because a JavaScript array is an object.

Solution 1:

To solve this problem ECMAScript 5 defines a new method Array.isArray():

Array.isArray(fruits); // returns true

The problem with this solution is that ECMAScript 5 is not supported in older browsers.

Solution 2:

To solve this problem you can create your own isArray() function:

function isArray(x) {
return x.constructor.toString().indexOf("Array") > -1;
}

The function above always returns true if the argument is an array.

Or more precisely: it returns true if the object prototype contains the word "Array".

Solution 3:

The instanceof operator returns true if an object is created by a given constructor:

var fruits = ["Banana", "Orange", "Apple", "Mango"];

fruits instanceof Array; // returns true

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Previous Next

JavaScript String Methods

String Methods And Properties

String Length

Example

Finding a String in a String

Example

Example

Example

Example

Example

Searching For A String In A String

Example

Did You Notice?

Extracting String Parts

The slice() Method

Example

Example

Example

Example

The substring() Method

Example

The substr() Method

Example

Example

Example

Replacing String Content

Example

Example

Example

Example

Example

Converting To Upper And Lower Case

Example

Example

The Concat() Method

Example

Example

String.trim()

Example

Example

Example

JavaScript String Padding

Example

Example

Converting A String To An Array

Example

Example

How To Recognize An Array

Solution 1:

Solution 2:

Solution 3:

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