JavaScript String Object

---

The String object is used for storing and manipulating text.

---

JavaScript Strings

A string simply stores a series of characters like "John Doe".

A string can be any text inside quotes. You can use single or double quotes:

Example

var carname="Volvo XC60";
var carname='Volvo XC60';

You can access each character in a string with its position (index):

Example

var character=carname[7];

String indexes are zero-based, which means the first character is [0], the second is [1], and so on.

You can use quotes inside a string, as long as they don't match the quotes surrounding the string:

Example

var answer="It's alright";
var answer="He is called 'Johnny'";
var answer='He is called "Johnny"';

Or you can put quotes inside a string by using the \ escape character:

Example

var answer='It\'s alright';
var answer="He is called \"Johnny\"";

---

String Length

The length of a string (a string object) is found in the built in property length:

Example

var txt="Hello World!";
document.write(txt.length);

var txt="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
document.write(txt.length);

---

Finding a String in a String

The indexOf() method returns the position (as a number) of the first found occurrence of a specified text inside a string:

Example

var str="Hello world, welcome to the universe.";
var n=str.indexOf("welcome");

The method returns -1 if the specified text is not found.

The lastIndexOf() method starts searching at the end of the string instead of at the beginning.

---

Matching Content

The match() method can be used to search for a matching content in a string:

Example

var str="Hello world!";
document.write(str.match("world") + "<br>");
document.write(str.match("World") + "<br>");
document.write(str.match("world!"));

---

Replacing 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");

---

Upper Case and Lower Case

A string is converted to upper/lower case with the methods toUpperCase() / toLowerCase():

Example

var txt="Hello World!";       // String
var txt1=txt.toUpperCase();   // txt1 is txt converted to upper
var txt2=txt.toLowerCase();   // txt2 is txt converted to lower

---

Convert a String to an Array

A string is converted to an array with the built in method string.split():

Example

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

---

Special Characters

The backslash (\) can be used to insert apostrophes, new lines, quotes, and other special characters into a string.

Look at the following JavaScript code:

var txt="We are the so-called "Vikings" from the north.";
document.write(txt);

In JavaScript, a string is started and stopped with either single or double quotes. This means that the string above will be chopped to: We are the so-called

To solve this problem, you must place a backslash (\) before each double quote in "Viking". This turns each double quote into a string literal:

var txt="We are the so-called \"Vikings\" from the north.";
document.write(txt);

JavaScript will now output the proper text string: We are the so-called "Vikings" from the north.

The table below lists other special characters that can be added to a text string with the backslash sign:

Code	Outputs
\'	single quote
\"	double quote
\\	backslash
\n	new line
\r	carriage return
\t	tab
\b	backspace
\f	form feed

---

Strings Can be Strings or Objects

JavaScript strings can be primitive values created from literals, like var x = "John";

JavaScript strings can also be objects created with the new keyword, like var y = new String("John");

Example

var x = "John";
var y = new String("John");
typeof(x) // returns String
typeof(y) // returns Object

Normally, because of some nasty side effects, you will not define strings as objects.

Example

var x = "John";             
var y = new String("John");
(x === y) // is false because x is a string and y is an object.

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

With JavaScript, all methods and properties of the string object are also available to primitive values, because Javascript will temporarily transfer primitive values to objects before executing the methods or properties.

---

String Properties and Methods

Properties:

• length
• prototype
• constructor

Methods:

• charAt()
• charCodeAt()
• concat()
• fromCharCode()
• indexOf()
• lastIndexOf()
• localeCompare()
• match()
• replace()
• search()
• slice()
• split()
• substr()
• substring()
• toLowerCase()
• toUpperCase()
• toString()
• trim()
• valueOf()