Searching for '\' using javascript

I have written a following code to get just the file name without extension and path.I m running it in browser.

<script type="text/javascript">
var str=new String("C:\Documents and Settings\prajakta\Desktop\substr.html");
document.write(str);
var beg=str.lastIndexOf("\");// **HERE IS THE PROBLEM IT DOESNT GIVE ME THE INDEX OF '\'**
 alert(beg);
var end=str.lastIndexOf (".");
 alert(end);
document.write("<br>"+str.slice(beg+1,end));开发者_如何学JAVA
</script> 

but the same code code works if i replace'\' by another character ex.('p'); i m initializing var str just for ex but in my application it is not always fixed.As i m new to Javascript can any body plz tell me what is the problem?n how to solve it?

You need to escape your backslash character. Use the following:

var beg=str.lastIndexOf("\\");

EDIT: Yes, it will give a -1 unless you escape the backslashes in your original string as well :)

Use this:

var str=new String("C:\\Documents and Settings\\prajakta\\Desktop\\substr.html");

Backslash is the Javascript escape character - this means that characters following a backslash refer to special characters. Thus, in your original string, \prajakta would be interpreted as '\p' + 'rajakta' where '\p' has a very different meaning. Thus, you need to use '\\' everywhere in every string.

"\" is the escape character, try with "\\"

Anyway, I would do it with regexes, just because I like them :)

var str=new String("C:\\Documents and Settings\\prajakta\\Desktop\\substr.html");
document.write(str);
document.write("<br>"+str.replace(/^.*\\/,"").replace(/\..*?$/,""));

Oh, and testing I saw that you have to escape the backslashes in the test string also!

You need to escape "\" in most languages, because \ is an escape-sequence. Javascript is probably the same.

Try searching for "\\" (without the space) instead. Also, replace "C:\Docume..." with "C:\\Documents..." for the same reason

Try

lastIndexOf("\\")

Before putting your string into the variable you should escape(String) it.

Backslash is generally the escape character, so you'll have to enter it twice whenever it occurs in a string, i.e. your

var str=new String("C:\Documents and Settings\prajakta\Desktop\substr.html");

should read

var str=new String("C:\\Documents and Settings\\prajakta\\Desktop\\substr.html");

The thing is, \D is interpreted by the javascript engine, and will be replaced by the appropriate special character (in this case, I don't believe there's a special character \D (or 'p' or 's'), so it'll be replaced by simply D, and your string contents will be

"C:Documents and SettingsprajaktaDesktopsubstr.html"

Go ahead, check it with a simple

if (str == "C:Documents and SettingsprajaktaDesktopsubstr.html") alert("Doh! :)");

it should give you the alert.

Also, your

var beg=str.lastIndexOf("\");

should read

var beg=str.lastIndexOf("\\");

HTH.

in addition to what's already said, "new String" makes no sense here

var str="C:\\Documents and Settings\\prajakta\\Desktop\\substr.html";

and yes, regexps are the way to go

fileName = str.match(/([^\\.]+)\.\w+$/)[1]