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I have a variable patt with a dynamic numerical value 

var patt = "%"+number+":";

What is the regex syntax for using it in the test() method?

I have been using this format

var patt=/testing/g;
var found = patt.test(textinput);

TIA

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3 Answers

up vote 1 down vote accepted

Yeah, you pretty much had it. You just needed to pass your regex string into the RegExp constructor. You can then call it's test() function.

var matcher = new RegExp("%" + number + ":", "g");
var found = matcher.test(textinput);

Hope that helps :)

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Thanks MicronXD, I was not aware of the regexp constructor. – Jamex Oct 12 '11 at 4:53
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up vote 5 down vote

You have to build the regex using a regex object, rather than the regex literal.

From your question, I'm not exactly sure what your matching criteria is, but if you want to match the number along with the '%' and ':' markers, you'd do something like the following:

var matcher = new RegExp("%" + num_to_match + ":", "g");

You can read up more here: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/RegExp

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Thanks Gopher, I was not aware of this command. – Jamex Oct 12 '11 at 4:52
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up vote 4 down vote

You're on the right track

var testVar = '%3:';

var num = 3;

var patt = '%' + num + ':';

var result = patt.match(testVar);

alert(result);

Example: http://jsfiddle.net/jasongennaro/ygfQ8/2/

You should not use number. Although it is not a reserved word, it is one of the predefined class/object names.

And your pattern is fine without turning it into a regex literal.

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Your example works because you have MooTools loaded. A String doesn't normally have a .test() method. And number is not a reserved word. – user113716 Oct 12 '11 at 4:19
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@Ӫ_._Ӫ You're so right!! Thinking in frameworks too much. I've edited to remove test() for match(). Thanks for the catch. Also, you're right about number not being a reserved word. Edited that too to be more clear. Typing to quickly without double-checking my facts. ;-) – Jason Gennaro Oct 12 '11 at 4:30
Thanks Jason for your effort to teach. – Jamex Oct 12 '11 at 4:56
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