Simple JavaScript String.replace.call results in "InternalError: too much recursion"

Question

Given the following JavaScript "class" definition:

var Quota = function(totalMinutes){
    this.totalMinutes = parseInt(totalMinutes || 0, 10);
};

Quota.prototype.valueOf = function(){
    return this.totalMinutes;
};

Quota.prototype.toString = function(format){
    format = format || "hh:mm";

    return format.replace.call(this, /hh?|mm?/g, function(match){
        switch (match) {
            case "hh":
                return this.totalMinutes * 60;
            case "mm":
                return this.totalMinutes;
        }
    });
};

Can you please explain exactly why the below call to toString()...

var q1 = new Quota(60);
console.log( q1.toString() );

...results in the following error being raised:

InternalError: too much recursion { message="too much recursion", more...}

I'm running the code (Firefox 3.5.7 + Firebug 1.5) in the Firebug Console. Ideally I'd like to know where is the recursive call back to toString() and your suggestions for how the replace function could be executed here via call or apply

Kobi · Accepted Answer · 2010-01-24 11:02:04Z

5

return format.replace.call(this, /hh?|mm?/g, function(match)

format.replace tries to call this.toString, which ends in an infinite recursion. As requested, here's a proof this happens: http://jsbin.com/eweli/:

var Quota = function(totalMinutes){
    this.totalMinutes = parseInt(totalMinutes || 0, 10);
};

Quota.prototype.toString = function(format){
    alert ("Quota.prototype.toString is called");
};

var q1 = new Quota(60);
var a = "string".replace.call(q1,'hello','world');

Try this instead:

return format.replace(/hh?|mm?/g, function(match)

Edit

Problems aside, the best way I've found to allow the function to access the current quota is to create a variable outside it's closure:

Quota.prototype.toString = function(format){
    format = format || "hh:mm";
    var quota = this;
    return format.replace(/hh|mm/g, function(match){
        switch (match) {
            case "hh":
                return quota.totalMinutes / 60;
            case "mm":
                return quota.totalMinutes;
        }
        return match;
    });
};

edited Jan 24, 2010 at 11:02

answered Jan 24, 2010 at 10:17

Kobi

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6 Comments

Peter McG Over a year ago

The first argument to call is just what to use as the this parameter, I don't see how toString is called again on q1? None of your solutions allow the calls to this.totalMinutes in the body of the inner function to resolve correctly either?

Kobi Over a year ago

@Peter - see test case to prove replace calls toString.

Peter McG Over a year ago

After edit: Yes there are lots of easier ways of writing the method. The question is more theory based: what I'm really trying to get to is how to call replace in this way and have the inner function be able to resolve this.totalMinutes to the instance of Quota, this is mentioned in the last sentence.

Peter McG Over a year ago

Interesting, I haven't seen any documentation that call calls toString on the object you pass as it's first parameter but your test case does indeed prove that it does. The question emphasised in my above comment remains outstanding?

Kobi Over a year ago

@Peter - call definitely does not call toString. replace is a string function, however, so it makes perfect sense it will call toString on its argument. I don't think you can control this on the function replace is getting though, it takes (match, index, full string). Maybe if you changed its prototype too, but now we're just being silly.

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