Question

I am trying to retrieve a part of a string from a URL using regex.exec()it but I am getting an error for some reason. Hoping you guys can spot it.

I am trying to get this from the string -> http://anotherdomain.com/image.jpg

var haystack = 'http://domain.com/?src=http://anotherdomain.com/image.jpg&h=300';
var needle = /(?<=src=).+(?=&h)/;
var results = needle.exec(haystack);

So on load I am getting this error -> SyntaxError: invalid quantifier

So I tried adding single quotes around the needle but didn’t work. Adding quotes gives me needle.exec is not a function.

Answer 1

Javascript regular expressions do not support lookbehind.

You might be able to get by with:

var haystack = 'http://domain.com/?src=http://anotherdomain.com/image.jpg&h=300';
var needle = /src=(.+)(?=&h)/;
var results = needle.exec(haystack);

// results is now ["src=http://anotherdomain.com/image.jpg", "http://anotherdomain.com/image.jpg"], so haystack[1] is what you want.