I want to get URLs of all images in multiline text (no matter what it contains).

This is my code:

var pattern = /(http:\/\/\S+\.(?:jpg|gif|png|jpeg|JPG|GIF|PNG|JPEG))/mg;
var testResult = pattern.test(str));
var result = pattern.exec(str);

If str equals ".jpg", testResult equals true but result is null. Why? Would you help me to solve this problem?

I want to get URLs of all images in multiline text (no matter what it contains).

This is my code:

var pattern = /(http:\/\/\S+\.(?:jpg|gif|png|jpeg|JPG|GIF|PNG|JPEG))/mg;
var testResult = pattern.test(str));
var result = pattern.exec(str);

If str equals "http://example.dom./-6/x_5eb0916a.jpg", testResult equals true but result is null. Why? Would you help me to solve this problem?

• javascript
• regex

• You have one ) too much at the end of line 2. Also what is str? It's undefined in your code. – js-coder Commented Jan 7, 2012 at 11:52
• 1 It could be helpful to add a \/ between your domain and file extension patterns, to prevent subdomains from being parsed otherwise http://some.png.example./home.html will give you http://some.png (I concede it's just a matter of principle ;) ). – Matteo B. Commented Jan 7, 2012 at 12:22

4 Answers 4

That's because of the g flag. If you invert the two calls, you'll get different results because the global flag sets pattern.lastIndex and starts matching from that index the next time you call .test/.exec. When inverting the calls, you'd get a non-null result for .exec, and false for .test.

With .lastIndex and the global flag, in your case it matches the URL for .test, and will start looking for more URLs after the first URL when you execute .exec. There are no more URLs, so you'll get null. Note that lastIndex is then reset to 0, so calling .exec again would work.

Anyhow, you seem to be looking for str.match(pattern) instead, which simply lists all matches:

var str = " test http://example.dom./-6/x_5eb0916a.jpg"
             + " \nfoo http://example2./test.png";

var pattern = /(http:\/\/\S+\.(?:jpg|gif|png|jpeg|JPG|GIF|PNG|JPEG))/gm;

str.match(pattern);
// ["http://example.dom./-6/x_5eb0916a.jpg", "http://example2./test.png"]

Solution to this issue is to simply set lastIndex of regex to zero.

var pattern = /(http:\/\/\S+\.(?:jpg|gif|png|jpeg|JPG|GIF|PNG|JPEG))/mg;
var testResult = pattern.test(str));
pattern.lastIndex=0;
var result = pattern.exec(str);
pattern.lastIndex=0;

Did you try this,

"http://example.dom./-6/x_5eb0916a.jpg".match(pattern)

also try returning a function that creates the regex instead of resetting the lastIndex each time.

function getRegex(){
  return /(http:\/\/\S+\.(?:jpg|gif|png|jpeg|JPG|GIF|PNG|JPEG))/mg;
}

const testResult = getRegex().test(str);