Javascript dynamic Regexp value

Question

I wanting to pass in a dynamic value for this regex but it's not working. I'm not sure what's missing from my code. I tried to escape the string but for some reason I missing something.

Any help is greatly appreciated.

var r = new RegExp('(?:^| )(myclass)(?: |$)'), m = (""+n.className).match(r); //found

var c = 'myclass';
var r = new RegExp("(?:^| )('\\b'" + c + "'\\b')(?: |$)"), m = (""+n.className).match(r); // not found

Edit --- when adding dynamic value (myclass) no node is returned. When it's hard coded I can find a node without issue.

 var n = document.getElementById('parentID');
 var c = 'myclass';

function find(n,c) {

do {
    if (typeof n.className !== 'undefined') {
        var r = new RegExp("(?:^| )(myclass)(?: |$)"), m = (""+n.className).match(r);
        if (m !== null) {
            n.setAttribute("id", "current");
        }
    }
    if (n.hasChildNodes()) {
        finds(n.firstChild)
    }
}
while (n = n.nextSibling)
}

it's an element = var n= document.getElementById('someDiv'); — user686483
– user686483, Commented Apr 9, 2014 at 11:48
thats okay but what is the value of n.classname? is it some string ? — aelor
– aelor, Commented Apr 9, 2014 at 12:07

aelor · Accepted Answer · 2014-04-09 12:10:51Z

1

try this :

var c = 'myclass';
var r = new RegExp("(?:^| )(\\b"+c+"\\b)(?: |$)");
console.log(r);

this will return the result as

RegExp /(?:^| )('\b'myclass'\b')(?: |$)/

suppose you dont want the \b on both sides of myclass then just use the code below :

var c = 'myclass';
var r = new RegExp("(?:^| )("+c+")(?: |$)");
console.log(r);

go ahead , fire your firebug, paste in it and hit Run

update

check this code its working:

var c = 'myclass';
var r = new RegExp("(?:^| )(\\b"+c+"\\b)(?: |$)");
console.log(r);

var str = "myclass";
var m = (""+str).match(r);
console.log(m);

edited Apr 9, 2014 at 12:10

answered Apr 9, 2014 at 11:59

aelor

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2 Comments

aelor Over a year ago

@user686483 what output are you expecting ?? can you give an example

user686483 Over a year ago

Hi @aelor: I'm using this in a re-usable js function: function find(n,c) { do { if (typeof n.className !== 'undefined') { var r = new RegExp("(?:^| )(myclass)(?: |$)"), m = (""+n.className).match(r); if (m !== null) { n.setAttribute("id", "current"); } } if (n.hasChildNodes()) { finds(n.firstChild) } } while (n = n.nextSibling) }

Peter Herdenborg · Accepted Answer · 2014-04-09 13:15:57Z

1

In the failing RegExp, you need to remove the single quotes around '\\b' I think.

EDIT: Fiddle at http://jsfiddle.net/UqL4J/ seems to suggest that your regexp with the single quotes removed does work as expected.

edited Apr 9, 2014 at 13:15

answered Apr 9, 2014 at 11:57

Peter Herdenborg

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3 Comments

user686483 Over a year ago

I did try this as well as many other combinations. It's something very simple I know but I just can't get the syntax right.

Peter Herdenborg Over a year ago

I just updated my answer with a fiddle that I hope is relevant.

user686483 Over a year ago

Hi Peter, I've verified it's working but now my function is returning #text as a node as apposed to <div class="myclass"> </div> which is what it was returning with the hardcoded value originally. So two different issues here.

the6p4c · Accepted Answer · 2014-04-09 11:48:52Z

0

I don't believe that you need to be adding the characters before and after where you add the value into the regex ('\\b'). Try using the line

var r = new RegExp("(?:^| )(" + c + ")(?: |$)"), m = (""+n.className).match(r);

which will expand to

(?:^| )(myclass)(?: |$)

which is the same as the first RegEx line.

answered Apr 9, 2014 at 11:48

the6p4c

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2 Comments

user686483 Over a year ago

I tried this but it's failing for some reason. If I have "(?:^| )(" + c + ")(?: |$)" it fails but if I have "(?:^| )(myclass)(?: |$)" it's fine.

the6p4c Over a year ago

@user686483 If you extract the string from the constructor and print it, what is the output?

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