Programming Tutorials

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Strings in JavaScript

By: aathishankaran in JavaScript Tutorials on 2007年03月29日 [フレーム]

Strings are a fundamental part of any programming language. Strings, which are a set of alpha-numeric characters, can be either a literal string, such as "Push the envelope" or a variable representing a string, such as the Phrase. A string can also be treated as an object, complete with its own suite of methods and properties.

Creating a String Object

Use the following procedure to create a string object.

var str_obj =new String([message])

Example:

<SCRIPT>
 var str = new String("My name is Richard" )
 alert (str. length)
</SCRIPT>

Working with Strings

Because strings are one of the primary types of data you have to work with, it is critical to have some way of extracting data from strings and obtaining information about strings. JavaScript has the properties and methods

Method/Property

Description

length

Returns an integer representing the value of size of the string.

charAt (pos)

Returns the character at the specified index.

indexOf (searchText [,startPos])

Returns the index of the first occurrence of SearchText.

lastIndexOf(searchText [,endPos])

Returns the index of last occurrence of searchText

substring (startPos, endPos)

Returns the substring of the string starting at startpos and ending at endPos

Determining String Lengths

You can use the String object's length property to determine the size of a string.

For example, the following code returns 17:

"Crazy Legs Nelson".length

The following code returns 16:

var str = "This is the day." 
len = str.length

Searching Within Strings

You can search for text within strings by using indexOf() and lastIndexOf(). Use these methods when you want to search for a particular character or substring within a string and return the position (or index) of the occurrence within the string. Whereas indexOf() starts at the left of the string and moves right, lastIndexOfO does the same operation but starts at the left. Both indexOf() and lastIndexOfO start at the 0 position for the first character encountered, and both return a value of -1 if the search text is not found. For example, the following code re-turns a value of 3:

"Time and time again".indexOf("e")

On the other hand, the following code returns a value of 12:

"Time and time again".lastIndexOf("e")

Both methods have an optional second parameter that enables you to specify here in the string you want to start the search. For example, the script shown n Listing 14.1 searches through the variable graf and counts the number of occurrences of the letter 'e'.

<SCRIPT>
	pos = 0 
	num = -1 
	i = -1
	var graf = "While nearly everyone agrees on the principle of reuse,
	the priority we give it varies wildly."
	while (pos != -1)
	{
	 pos = graf.indexOf("e",i+1)
	 num += 1
	 i = pos
	}
document.write(graf)
document.write("<p><p>")
document.write("There were" + num + " e' s in that paragraph.")
</SCRIPT>

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