Book Image

Object-Oriented JavaScript

By : Stoyan Stefanov, Stoyan STEFANOV
Book Image

Object-Oriented JavaScript

By: Stoyan Stefanov, Stoyan STEFANOV

Overview of this book

Table of Contents (18 chapters)
Object-Oriented JavaScript
Credits
About the Author
About the Reviewers
Preface
Built-in Functions
Regular Expressions
Index

String


The String() constructor creates string objects. Primitive strings are turned into objects behind the scenes if you call a method on them as if they were objects.

Creating a string object and a string primitive:

>>> var s_obj = new String('something'); 
>>> var s_prim = 'something';
>>> typeof s_obj

"object"

>>> typeof s_prim

"string"

The object and the primitive are not equal when compared by type with ===:

>>> s_obj === s_prim

false

>>> s_obj == s_prim

true

length is a property of string objects:

>>> s_obj.length

9

If you access length on a non-object but a primitive string, the primitive is converted to an object behind the scenes and the operation is successful:

>>> "something".length

9

Members of the String Constructor

Property/Method

Description

String.fromCharCode (code1, code2, code3, ...)

Returns a string created using the input character codes:

>>> String.fromCharCode(115, 99, 114, 105, 112, 116);

"script"

Members of the String Objects

Property/Method

Description

length

The number of characters in the string.

>>> new String('four').length

4

charAt(pos)

Returns the character at the specified position. Positions start at 0.

>>> "script".charAt(0);

"s"

charCodeAt(pos)

Returns the code of the character at the specified position.

>>> "script".charCodeAt(0);

115

concat(str1, str2, ....)

Return a new string glued from the input pieces.

>>> "".concat('zig', '-', 'zag');

"zig-zag"

indexOf(needle, start)

If the needle matches a part of the string, the position of the match is returned. The optional second parameter tells where the search should start from. Returns -1 if no match is found.

>>> "javascript".indexOf('scr')

4

>>> "javascript".indexOf('scr', 5)

-1

lastIndexOf(needle, start)

Same as indexOf() but starts the search from the end of the string. The last occurence of "a":

>>> "javascript".lastIndexOf('a') 

3

localeCompare(needle)

Compares two strings in the current locale. Returns 0 if the two strings are equal, 1 if the needle gets sorted before the string object, -1 otherwise.

>>> "script".localeCompare('crypt')

1

>>> "script".localeCompare('sscript')

-1

>>> "script".localeCompare('script')

0

match(regexp)

Accepts a regular expression object and returns an array of matches.

>>> "R2-D2 and C-3PO".match(/[0-9]/g)

["2", "2", "3"]

replace(needle, replacement)

Allows you to replace the matching results of a regexp pattern. The replacement can also be a callback function. Capturing patterns are available as $1, $2,...$9.

>>> "R2-D2".replace(/2/g, '-two')

"R-two-D-two"

>>> "R2-D2".replace(/(2)/g, '$1$1')

"R22-D22"

search(regexp)

Returns the position of the first regular expression match.

>>> "C-3PO".search(/[0-9]/)

2

slice(start, end)

Returns the part of a string identified by start and end position. If start is negative, then the start position is length + start, similarly if the end parameter is negative, the end position is length + end.

>>> "R2-D2 and C-3PO".slice(4,13)

"2 and C-3"

>>> "R2-D2 and C-3PO".slice(4,-1)

"2 and C-3P"

split(separator, limit)

Turns a string into an array. The second parameter, limit, is optional. The separator can also be a regular expression.

>>> "1,2,3,4".split(',')

["1", "2", "3", "4"]

>>> "1,2,3,4".split(',', 2)

["1", "2"]

substring(start, end)

Similar to slice(). When start or end are negative or invalid, they are considered 0. If they are greater than the string length, they are considered to be the length. If end > start, their values are swapped.

>>> "R2-D2 and C-3PO".substring(4, 13)

"2 and C-3"

>>> "R2-D2 and C-3PO".substring(13, 4)

"2 and C-3"

toLowerCase()

toLocaleLowerCase()

Transforms the string to lower case.

>>> "JAVA".toLowerCase()

"java"

toUpperCase()

toLocaleUpperCase()

Transforms the string to upper case.

>>> "script".toUpperCase()

"SCRIPT"