Built-in Object in Javascript
By: aathishankaran
String Object
Strings area 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 LANGUAGE = "JavaScript">
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 |
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 LANGUAGE =
"JavaScript">
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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