JavaScript strings are used for storing and manipulating text.
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:
You can use quotes inside a string, as long as they don't match the quotes surrounding the string:
The length of a string is found in the built in property length:
Because strings must be written within quotes, JavaScript will misunderstand this string:
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:
The escape character (\) can also be used to insert other special characters in a string.
This is the lists 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 |
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:
You can also break up a code line within a text string with a single backslash:
However, you cannot break up a code line with a backslash:
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")
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Don't create strings as objects.
It slows down execution speed, and produces nasty side effects: |
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When using the == equality operator, equal strings looks equal:
When using the === equality operator, equal strings are not equal:
The === operator expects equality in both type and value.
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.
| 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 |
| 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 |
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