JavaScript Strings
JavaScript strings are used to store and handle text.
JavaScript Strings
A string can store a series of characters, such as "John Doe".
A string can be any character enclosed in quotes. You can use single or double quotes:
Example
var carname = 'Volvo XC60';
You can use index positions to access each character in a string:
Example
String indexes start from 0, meaning the index value of the first character is[0], the second is[1], and so on.
Example
let letter = name[2];
document.getElementById("demo").innerHTML = letter;
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You can use quotes inside a string, as long as they don't match the quotes surrounding the string:
Example
var answer = "He is called 'Johnny'";
var answer = 'He is called "Johnny"';
You can also use escape characters to add quotes within a string:
String Length
The built-in propertylengthcan be used to calculate the length of a string:
Special Characters
In JavaScript, strings are written inside single or double quotes.
Because of this, JavaScript cannot parse the following example:
The string "We are the so-called " is truncated.
How to solve the problem above? You can use a backslash (\) to escape the double quotes in the "Vikings" string, as follows:
The backslash is anescape character. The escape character converts special characters into string characters:
The escape character (\) can be used to escape apostrophes, newlines, quotes, and other special characters.
The table below lists the special characters that can be escaped using escape characters in strings:
| Code | Output |
|---|---|
| \' | Single quote |
| \" | Double quote |
| \\ | Backslash |
| \n | Newline |
| \r | Carriage return |
| \t | Tab |
| \b | Backspace |
| \f | Form feed |
Strings Can Be Objects
Normally, JavaScript strings are primitive values, created using literals:var firstName = "John"
But we can also define a string as an object using the new keyword:var firstName = new String("John")
Example
var y = new String("John");
typeof x // returns String
typeof y // returns Object
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 |
Don't create String objects. It slows down execution speed and may produce other side effects: |
|---|
Example
var y = new String("John");
(x === y) // result is false, because x is a string and y is an object
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=== means absolute equality, i.e., both the data type and the value must be equal.
String Properties and Methods
Primitive value strings, such as "John", have no properties or methods (because they are not objects).
Primitive values can use JavaScript's properties and methods, because JavaScript can treat primitive values as objects when executing methods and properties.
We will introduce string methods in the next chapter.
String Properties
| Property | Description |
|---|---|
| constructor | Returns the function that created the string property |
| length | Returns the length of the string |
| prototype | Allows you to add properties and methods to objects |
String Methods
For more method examples, see:JavaScript String 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() | Connects two or more strings and returns the connected string |
| fromCharCode() | Converts Unicode to a string |
| indexOf() | Returns the position of the first occurrence of the specified character in the string |
| lastIndexOf() | Returns the position of the last occurrence of the specified character in the string |
| localeCompare() | Compares two strings in a locale-specific order |
| match() | Finds one or more matches of a regular expression |
| replace() | Replaces substrings that match a regular expression |
| search() | Retrieves the value that matches a regular expression |
| slice() | Extracts a section of a string and returns the extracted part in a new string |
| split() | Splits a string into an array of substrings |
| substr() | Extracts a specified number of characters from a starting index in the string |
| substring() | Extracts characters between two specified indexes in a string |
| toLocaleLowerCase() | Converts a string to lowercase according to the host's locale; only a few languages (such as Turkish) have locale-specific case mappings |
| toLocaleUpperCase() | Converts a string to uppercase according to the host's locale; only a few languages (such as Turkish) have locale-specific case mappings |
| toLowerCase() | Converts a string to lowercase |
| toString() | Returns the string object value |
| toUpperCase() | Converts a string to uppercase |
| trim() | Removes whitespace from both ends of a string |
| valueOf() | Returns the primitive value of a string object |