JavaScript Strings

JavaScript strings are used for storing and manipulating text.

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JavaScript Strings

A JavaScript 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 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"';

 

String Length

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

Example

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

 

Special Characters

Because strings must be written within quotes, JavaScript will misunderstand this string:

var y = "We are the so-called "Vikings" from the north."

The string will be chopped to "We are the so-called ".
The solution to avoid this problem, is to use the \ escape character.
The backslash escape character turns special characters into string characters:

Example

var x = 'It\'s alright';
var y = "We are the so-called \"Vikings\" from the north."

 

The escape character (\) can also be used to insert other special characters in a string.
This is the list of 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

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Breaking Long Code Lines

For best readability, programmers often like to avoid code lines longer than 80 characters.
If a JavaScript statement does not fit on one line, the best place to break it is after an operator:

Example

document.getElementById("demo").innerHTML =
"Hello Dolly.";

 

You can also break up a code line within a text string with a single backslash:

Example

document.getElementById("demo").innerHTML = "Hello \
Dolly!"; 

 

The safest (but a little slower) way to break a long string is to use string addition:

Example

document.getElementById("demo").innerHTML = "Hello" +
"Dolly!"; 

 

You cannot break up a code line with a backslash:

Example

document.getElementById("demo").innerHTML = \
"Hello Dolly!"; 

 

Strings Can be Objects

Normally, JavaScript strings are primitive values, created from literals: var firstName = "John"
But strings can also be defined as objects with the keyword new: var firstName = new String("John")

Example

var x = "John";
var y = new String("John");

// typeof x will return string// typeof y will return object

 

When using the == equality operator, equal strings looks equal:

Example

var x = "John";            
var y = new String("John");

// (x == y) is true because x and y have equal values 

 

When using the === equality operator, equal strings are not equal, because the === operator expects equality in both type and value.

Example

var x = "John";            
var y = new String("John");

// (x === y) is false because x and y have different types 

 

Or even worse. Objects cannot be compared:

Example

var x = new String("John");            
var y = new String("John");

// (x == y) is false because objects cannot be compared 

 

String Properties and Methods

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 methods are covered in next chapter.

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String Properties

Property	Description
constructor	Returns the function that created the String object's prototype
length	Returns the length of a string
prototype	Allows you to add properties and methods to an object

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String Methods

Method	Description
charAt()	Returns the character at the specified index (position)
charCodeAt()	Returns the Unicode of the character at the specified index
concat()	Joins two or more strings, and returns a copy of the joined strings
fromCharCode()	Converts Unicode values to characters
indexOf()	Returns the position of the first found occurrence of a specified value in a string
lastIndexOf()	Returns the position of the last found occurrence of a specified value in a string
localeCompare()	Compares two strings in the current locale
match()	Searches a string for a match against a regular expression, and returns the matches
replace()	Searches a string for a value and returns a new string with the value replaced
search()	Searches a string for a value and returns the position of the match
slice()	Extracts a part of a string and returns a new string
split()	Splits a string into an array of substrings
substr()	Extracts a part of a string from a start position through a number of characters
substring()	Extracts a part of a string between two specified positions
toLocaleLowerCase()	Converts a string to lowercase letters, according to the host's locale
toLocaleUpperCase()	Converts a string to uppercase letters, according to the host's locale
toLowerCase()	Converts a string to lowercase letters
toString()	Returns the value of a String object
toUpperCase()	Converts a string to uppercase letters
trim()	Removes whitespace from both ends of a string
valueOf()	Returns the primitive value of a String object