Is there a version of JavaScript's String.indexOf() that allows for regular expressions?

Instances of the String constructor have a .search() method which accepts a RegExp and returns the index of the first match.

To start the search from a particular position (faking the second parameter of .indexOf()) you can slice off the first i characters:

str.slice(i).search(/re/)

But this will get the index in the shorter string (after the first part was sliced off) so you'll want to then add the length of the chopped off part (i) to the returned index if it wasn't -1. This will give you the index in the original string:

function regexIndexOf(text, re, i) {
    var indexInSuffix = text.slice(i).search(re);
    return indexInSuffix < 0 ? indexInSuffix : indexInSuffix + i;
}

Combining a few of the approaches already mentioned (the indexOf is obviously rather simple), I think these are the functions that will do the trick:

function regexIndexOf(string, regex, startpos) {
    var indexOf = string.substring(startpos || 0).search(regex);
    return (indexOf >= 0) ? (indexOf + (startpos || 0)) : indexOf;
}

function regexLastIndexOf(string, regex, startpos) {
    regex = (regex.global) ? regex : new RegExp(regex.source, "g" + (regex.ignoreCase ? "i" : "") + (regex.multiLine ? "m" : ""));
    if(typeof (startpos) == "undefined") {
        startpos = string.length;
    } else if(startpos < 0) {
        startpos = 0;
    }
    var stringToWorkWith = string.substring(0, startpos + 1);
    var lastIndexOf = -1;
    var nextStop = 0;
    while((result = regex.exec(stringToWorkWith)) != null) {
        lastIndexOf = result.index;
        regex.lastIndex = ++nextStop;
    }
    return lastIndexOf;
}

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UPDATE: Edited regexLastIndexOf() so that is seems to mimic lastIndexOf() now. Please let me know if it still fails and under what circumstances.

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UPDATE: Passes all tests found on in comments on this page, and my own. Of course, that doesn't mean it's bulletproof. Any feedback appreciated.

I have a short version for you. It works well for me!

var match      = str.match(/[abc]/gi);
var firstIndex = str.indexOf(match[0]);
var lastIndex  = str.lastIndexOf(match[match.length-1]);

And if you want a prototype version:

String.prototype.indexOfRegex = function(regex){
  var match = this.match(regex);
  return match ? this.indexOf(match[0]) : -1;
}

String.prototype.lastIndexOfRegex = function(regex){
  var match = this.match(regex);
  return match ? this.lastIndexOf(match[match.length-1]) : -1;
}

EDIT : if you want to add support for fromIndex

String.prototype.indexOfRegex = function(regex, fromIndex){
  var str = fromIndex ? this.substring(fromIndex) : this;
  var match = str.match(regex);
  return match ? str.indexOf(match[0]) + fromIndex : -1;
}

String.prototype.lastIndexOfRegex = function(regex, fromIndex){
  var str = fromIndex ? this.substring(0, fromIndex) : this;
  var match = str.match(regex);
  return match ? str.lastIndexOf(match[match.length-1]) : -1;
}

To use it, as simple as this:

var firstIndex = str.indexOfRegex(/[abc]/gi);
var lastIndex  = str.lastIndexOfRegex(/[abc]/gi);