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String class

The String class

The

String

class is the object representation of a String primitive and is created in the following manner:

var oStringObject = new String(“hello world”);

Both

valueOf()

and

toString()

return the String primitive value for a

String

object:

alert(oStringObject.valueOf() == oStringObject.toString()); //outputs “true”

If you run this code, the output is

“true”

, indicating that the values are indeed equal.

The

String

class is one of the more complicated reference types in ECMAScript. As such, this section

focuses only on the basic functionality of the

String

class. More advanced functionality is split into

suitable topics throughout the book.

The

String

class has one property,

length

, which gives the number of characters in the string:

var oStringObject = new String(“hello world”);

alert(oStringObject.length); //outputs “11”

This example outputs

“11”

, the number of characters in

“hello world”

. Note that even if the string

contains a double-byte character (as opposed to an ASCII character, which uses just one byte), each char-

acter is still counted as one.

The

String

class also has a large number of methods. The first two,

charAt()

and

charCodeAt()

have to do with accessing the individual characters in the string. As described in the section on String

primitives, the first character is in position 0, the second is in position 1, and so on. Both these methods

accept one argument, the position of the character to act on. The

charAt()

method returns a string con-

taining the character in that position:

var oStringObject = new String(“hello world”);

alert(oStringObject.charAt(1)); //outputs “e”

The character in position 1 of

“hello world”

“e”

, so calling

charAt(1)

returns

“e”

. If instead of the

actual character you want the character code, then calling

charCodeAt()

is the appropriate choice:

var oStringObject = new String(“hello world”);

alert(oStringObject.charCodeAt(1)); //outputs “101”

This example outputs

“101”

, which is the character code for the lowercase

character.

Similar to the

Boolean

object, the

Number

object is important, but it should be used

sparingly in order to avoid potential problems. Whenever possible, you should use

numeric primitives instead.

ECMAScript Basics

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