JavaScript string

JavaScript strings are used to store and process text.

JavaScript String

A string can store a sequence of characters, such as "John Doe".

The string can be any character inserted into the quotes. You can use single or double quotes:

Example

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

You can use the index position to access each character in the string:

Example

var character = carname[7];

The index of the string starts from 0, which means that the first character index value is [0], the second is [1], and so on.

You can use quotation marks in the string. The quotation marks in the string should not be the same as the quotation marks in the string:

Example

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

You can also add escapes to the string characters to use quotation marks:

Instance

<!DOCTYPE html>
<html>
<head> 
<meta charset="utf-8"> 
<title>php中文网(php.cn)</title> 
</head>
<body>

<p id="demo"></p>
<script>
var x = 'It\'s alright';
var y = "He is called \"Johnny\"";
document.getElementById("demo").innerHTML = x + "<br>" + y; 
</script>

</body>
</html>

Run Instance»

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String length

You can use the built-in property length to calculate the length of a string:

Example

<!DOCTYPE html>
<html>
<head> 
<meta charset="utf-8"> 
<title>php中文网(php.cn)</title> 
</head>
<body>

<script>
var txt = "Hello World!";
document.write("<p>" + txt.length + "</p>");
var txt="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
document.write("<p>" + txt.length + "</p>");
</script>

</body>
</html>

Run instance»

Click the "Run instance" button to view the online instance

Special characters

In JavaScript, strings are written in single quotes or double quotes.

Because of this, the following example JavaScript cannot be parsed: x

"We are the so-called "Vikings" from the north."

The string "We are the so-called " is truncated.

How to solve the above problems? You can use backslash (\) to escape double quotes in the "Vikings" string, as follows:

"We are the so-called \"Vikings\" from the north."

The backslash is a escape character . Escape characters convert special characters into string characters:

The escape character (\) can be used to escape apostrophes, newlines, quotation marks, and other special characters.

The following table lists the special characters that can be escaped using escape characters in strings:

##\ rEnter##\t\b\f

Code	Output
\'	Single quotes
\"	Double quotes
\\	Backslash
\n	Newline

tab(tab)
Backspace character
Form feed character

String is OK is an object

Normally, JavaScript strings are primitive values and can be created using characters:

var firstName = "John"

But we can also use the new keyword to add characters A string is defined as an object:

var firstName = new String("John")

Instance

<!DOCTYPE html>
<html>
<head> 
<meta charset="utf-8"> 
<title>php中文网(php.cn)</title> 
</head>
<body>
	
<p id="demo"></p>
<script>
var x = "John";              // x是一个字符串
var y = new String("John");  // y是一个对象
document.getElementById("demo").innerHTML =typeof x + " " + typeof y;
</script>

</body>
</html>

Run Instance»
Click the "Run Instance" button See online examples

Do not create String objects. It slows down execution and may have other side effects:

Example

<!DOCTYPE html>
<html>
<head> 
<meta charset="utf-8"> 
<title>php中文网(php.cn)</title> 
</head>
<body>
	
<p id="demo"></p>
<script>
var x = "John";              // x 是字符串
var y = new String("John");  // y 是一个对象
document.getElementById("demo").innerHTML = x===y;
</script>
<p>=== 为绝对相等，即数据类型与值都必须相等。</p>
	
</body>
</html>

Run Example»
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=== is absolutely equal, that is, the data type and value must be equal.

String properties and methods

Primitive value strings, such as "John", have no properties and methods (because they are not objects).

Primitive values can use JavaScript properties and methods, because JavaScript can treat primitive values as objects when executing methods and properties.

String methods we will introduce in the next chapter.

String attribute

Attribute constructor#length prototype

String Method

Description
Returns the function that creates the string property
Returns the length of the string
Allows you to add properties and methods to an object

Method	Description
charAt()	Returns the character at the specified index position
charCodeAt()	Returns the Unicode value of the character at the specified index position
concat()	Concatenate two or more strings and return the concatenated string
fromCharCode()	Convert Unicode to characters String
indexOf()	Returns the position where the specified character appears for the first time in the string
lastIndexOf()	Returns the position of the last occurrence of the specified character in the string
localeCompare()	Compares two strings in a local-specific order
match()	Find a match for one or more regular expressions
replace()	Replace the substring that matches the regular expression
search()	Retrieve the value that matches the regular expression
slice()	Extract a fragment of the string and return the extracted part in a new string
split()	Split the string into an array of substrings
substr()	Extract the specified number of characters from the string from the starting index number
substring()	Extract the characters between two specified index numbers in the string
toLocaleLowerCase()	Convert a string to lowercase based on the host's locale. Only a few languages (such as Turkish) have local-specific case mapping
toLocaleUpperCase()	according The host's locale converts the string to uppercase, and only a few languages (such as Turkish) have local-specific case mapping
toLowerCase()	Convert the string to lowercase
toString()	Return the string object value
toUpperCase()	Convert the string to uppercase
trim()	Remove the leading and trailing blanks of the string
valueOf()	Return the original value of a string object

JavaScript string