About Java Script Regular Expressions

[Shashi Kala]

Hi,
I am new to Java Script.I wrote a code like...

var reg=new RegExp("/^13[\d]{9}$/");
document.writeln(reg.test("13123456789"));

I am getting "false" as result. Can anybody say me what is happening here? Why the string in test() function don't match with this pattern? and also give an example string, which matches this pattern.

Thanks in advance..

--Shashi

[Eric Pascarello]

When you use RegExp, you do not have to include / at the beginning or at the end. If you use \, you need to escape it.

With that said, your regular expression would look like this:

var reg=new RegExp("^13[\\d]{9}$");

Now if you want to limit the keystrokes and avoid using RegExp, which is slower, you can do something like this:

var reg = /^13\d{9}$/;

Eric

[Shashi Kala]

Thank You Eric,

Now I tried using the code as you said, still I am getting "false" only. What would be the problem??

And I am having one more doubt too..

code
----------------------------------------------------
var reg=/[0-9a-zA-Z\._-]/;
document.writeln(reg.test("abcd&%"));
document.writeln(reg.test("&%"));
----------------------------------------------------

In case of first writeln() function, I am getting "true" as result(But my expected result is "false"). And in the second writeln() function I am getting "false".

Can you please say me what actually the pattern /[0-9a-zA-Z\._-]/ means?

[Eric Pascarello]

I just ran this:

var reg1 = /^13\d{9}$/;
var reg2 = new RegExp("^13[\\d]{9}$");
 
var str1 = "13123456789";
var str2 = "23123456789";
 
alert(reg1.test(str1) + "\n" + reg2.test(str1));
alert(reg1.test(str2) + "\n" + reg2.test(str2));

And I get
true
true

and

false
false

So they work for me. You copying the code right?

Eric

[Eric Pascarello]

 var reg=/[0-9a-zA-Z\._-]/;
document.writeln(reg.test("abcd&%"));
document.writeln(reg.test("&%"));

The first one is true because it does make a match. It is matching abcd. You did not tell the regular expression it had to match the entire string. You said it has to match any of those characters.

If you would add start of string [^] and end of string [$] to it, plus say it has to be there one or more time [+]
var reg=/^[0-9a-zA-Z\._-]+$/;

You would get false because it has to match the whole thing. What does it mean? It has to match any of those characters.

I really think you need to do some reading on this stuff.

Here is an article on them: http://www.webreference.com/js/column5/

Eric

[Shashi Kala]

Thank you Eric,

I tried the code as you said. I got results good. Again Thank you for sending me a link to learn regular expressions.


--------
Shashi Kala