[JavaScript tutorial] JavaScript string

JavaScript strings are used to store and process text.

JavaScript string

JavaScript strings are used to store and process text.

JavaScript string

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

A string can be any character inserted into quotation marks. You can use single or double quotation marks:

Instance

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

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

Instance

var character = carname[7];

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

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

Instance

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 quotation marks:

Instance

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

String Length

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

Instance

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

Special characters

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

As a result, the following example of JavaScript cannot be parsed: x

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

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

How can we solve the above problems? You can use a backslash (\) to escape the double quotation marks in the "Vikings" string, as shown below:

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

A backslash is an escape character. Escape characters convert special characters to string characters:

Escape Character (\) can be used to escape character, line feed, quotation marks, and other special characters.

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

Code

Output

\ 'Single quotes

\ "Double quotation marks

\ Backslash

\ N line feed

\ R press ENTER

\ T tab (tab)

\ B Return character

\ F page feed

A string can be an object.

Generally, JavaScript strings are original values and can be created using characters: var firstName = "John"

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

Instance

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

Do not create a String object. It slows down execution and may produce other side effects:

Instance

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

String attributes and Methods

The original value string, such as "John", has no attributes and methods (because they are not objects ).

The original values can use JavaScript attributes and methods, because JavaScript can treat the original values as objects when executing methods and properties.

We will introduce the string method in the next section.

String attribute

Attribute

Description

Constructor returns the function used to create the string attribute.

Length returns the length of the string.

Prototype allows you to add attributes and methods to an 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 () connects two or more strings and returns the connected strings.

FromCharCode () converts a character to a Unicode Value

IndexOf () returns the position of the first occurrence of a specified character in a string.

LastIndexOf () returns the position of the last occurrence of a specified character in a string.

LocaleCompare () compares two strings in a specific local order.

Match () finds matching of one or more regular expressions

Replace () replaces the substring that matches the regular expression.

Search () searches for values that match Regular Expressions

Slice () extracts the string segment and returns the extracted part in the new string.

Split () Splits a string into a substring array.

Substr () extracts a specified number of characters from the start index number.

Substring () extracts the characters between two specified index numbers in the string.

ToLocaleLowerCase () converts strings to lowercase Based on the host's language environment. Only a few languages (such as Turkish) have local-specific case ing.

ToLocaleUpperCase () converts strings to uppercase Based on the host's language environment. Only a few languages (such as Turkish) have local-specific case ing.

ToLowerCase () converts string to small

ToString () returns the value of a string object.

ToUpperCase () converts string to uppercase

Trim () removes the white space at the beginning and end of the string.

ValueOf () returns the original value of a string object.

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