JavaScript string

JavaScript strings are used to store and process text.

JavaScript String

String can store a series of characters, such as "liu qi".

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

var carname = "double quote";
var carname = 'single quote';

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

var character = carname[7];

The index of the string starts from 0, which means that the first 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:

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

You can also add escape characters to the string to use quotes:

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

Run the program and try it

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 the program to try it out

Special characters

In JavaScript, strings are written in single 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."

Backslash is an 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:

## \ nLine feed## \r \t \b \f

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

Enter
tab(tab character)
Backspace character
Form feed character

Strings can be objectsNormally, JavaScript strings are primitive values, It can be created using characters: var firstName = "John"

But we can also use the new keyword to define the string as an object: var firstName = new String("John")

<!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 the program and try it

Note

: Do not create a String object. It will slow down execution and may have other side effects:

<!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 the program and try it

=== 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 convert primitive values when executing methods and properties. As an object.

String methods we will introduce in the following chapters

##String properties

##Property

DescriptionconstructorReturns a function that creates a string propertylengthReturns the length of the stringprototypeAllows you to add properties and methods to the object

String method

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()	Connect two Or multiple strings, return the concatenated string
fromCharCode()	Convert Unicode to a string
indexOf()	Returns the position where the specified character appears for the first time in the string
lastIndexOf()	Returns the position where the specified character appears in the string The position of the last occurrence of a character
localeCompare()	Compares two strings in locale-specific order
match()	Find a match for one or more regular expressions
replace()	Replace the substring that matches the regular expression
search()	Retrieve values that match 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 the two specified index numbers in the string
toLocaleLowerCase()	Convert the string to lowercase according to the locale of the host, Only a few languages (such as Turkish) have local-specific case mapping
toLocaleUpperCase()	Convert a string to uppercase according to the host's locale, only Several languages (such as Turkish) have local-specific case mapping
toLowerCase()	Convert a 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 value of a string object Original value

Continuing Learning

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<!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>

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