Iterate through regular expression array in Javascript

Question

How can I use an array of Regex expressions and iterate that array with 'exec' operation. I did initialize an array with various regular expressions like this:

var arrRegex = new Array(/(http:\/\/(?:.*)\/)/g, /(http:\/\/(?:.*)\/)/g);

Now I created a for loop that does this:

 for(i=0;i<arrRegex.length;i++){
     arrRegex[i].exec(somestring);
 }

The thing is that this doesn't seems to work. I don't want to use it hardcoded like this:

  (/(http:\/\/(?:.*)\/)/g).exec(somestring);

When using the array option, the '.exec' function returns null. When I use the hardcoded option it returns the matches as I wanted.

the exec doesn't return the matches as it should, but with the hard coded it does. matches = null — Liron Harel
– Liron Harel, Commented Jul 15, 2012 at 11:37

Dreen · Accepted Answer · 2012-07-15 11:56:10Z

2

The exec() returns the match so you should be able to capture it.

somestring = 'http://stackoverflow.com/questions/11491489/iterate-through-regular-expression-array-in-javascript';
var arrRegex = new Array(/(http:\/\/(?:.*)\/)/g, /(http:\/\/(?:.*)\/)/g);
for (i = 0; i < arrRegex.length; i++) {
    match = arrRegex[i].exec(somestring);
}

match is an array, with the following structure:

{
    [0] = 'string matched by the regex'
    [1] = 'match from the first capturing group'
    [2] = 'match from the second capturing group'
    ... and so on
}

Take a look at this jsFiddle http://jsfiddle.net/HHKs2/1/

You can also use test() instead of exec() as a shorthand for exec() != null. test() will return a boolean variable depending on whether the regex matches part of the string or not.

edited Jul 15, 2012 at 11:56

answered Jul 15, 2012 at 11:46

Dreen

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5 Comments

Liron Harel Over a year ago

I know that, and it worked beautifully when hardcoded, but returns null when I use the regex in the array like you wrote in your code. I use it on chrome browser

Dreen Over a year ago

Take a look at the jsFiddle link I posted, it uses the array way and returns results. Or are you referring to initialising the expressions from a string? Btw, you can also use test() instead of exec() as a shorthand for exec() != null. test() will return a boolean variable depending on whether the regex matches part of the string or not.

Liron Harel Over a year ago

if what you are saying is right, how come test here returns false: jsfiddle.net/IdanShechter/uLMBL

apsillers Over a year ago

@Dareen: It's important to note that match only retruns match groups if the regex is non-global. If the regex is global, it returns an array of whole matches only.

Dreen Over a year ago

@IdanShechter: Thats because the exec() modifies the properties of the regular expression object. Note that if you remove it, test() will return true: jsfiddle.net/uLMBL/1

Dio F · Accepted Answer · 2012-07-15 11:54:26Z

2

What you probably want to do is to capture the first group:

for(i=0;i<arrRegex.length;i++){
  var someotherstring = arrRegex[i].exec(somestring)[1];
  // do something with it ...
}

BTW: That is my guess, not sure what you are trying to do. But if you are trying to get the host name of a URL you should use /(http:\/\/(?:.?)\/)/g. The question mark after .* makes the previous quantifier (*) ungreedy.

answered Jul 15, 2012 at 11:54

Dio F

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2 Comments

Liron Harel Over a year ago

how come the test() function returns false, it should return true because there are matches jsfiddle.net/IdanShechter/uLMBL

Dio F Over a year ago

Well, your code is working here - even in Chrome. Could you give us a bit more context, like the left hand assignment of the exec() result. Or you could just provide your the actual relevant code you are working on.

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