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 JavaScript String Methods JAVASCRIPT

JavaScript String Methods  


JavaScript String Methods

String Length

The length property returns the length of a string:

Example

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

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");

Note: JavaScript counts positions from zero.

JavaScript - lastIndexOf()

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

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

Example

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

indexOf(), and lastIndexOf()

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

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

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

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);

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");

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).

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).

Example

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

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.

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

JavaScript - slice() Method with single parameters

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

var res = str.slice(7);

or, counting from the end.

var res = str.slice(-12);

Example

var res = str.slice(7);
 
var res = str.slice(-12) 

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);

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.

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(7,6);

var res = str.substr(7);

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", "W3Schools");

Converting to Upper and Lower Case

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

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

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

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

 

Example

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

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

The concat() Method

concat() joins two or more strings.

Example

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

String.trim()

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

Example

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

You can use replace() with a regular expression instead:

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:

 

Extracting String Characters

There are 3 methods for extracting string characters:

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

The charAt() Method

The charAt() method returns the character at a specified index (position) in a string.

Example

var str = "HELLO WORLD";
str.charAt(0);            // returns H

The charCodeAt() Method

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

var str = "HELLO WORLD";
str.charCodeAt(0);         // returns 72

Property Access

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

Example

var str = "HELLO WORLD";
str[0];                   // returns H

Property access might be a little unpredictable:

  • It does not work in Internet Explorer 7 or earlier
  • 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

var str = "HELLO WORLD";
str[0] = "A";           // Gives no error, but does not work
str[0];                   // returns H

Converting a String to an Array

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

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

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

Example

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

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

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