JS code running into infinite loop

Question

Here is the code, when I run it it is going to infinite loop, any flaws in code?

function s4() {
  return Math.floor((1 + Math.random()) * 0x10000).toString(16).substring(1);
};

function guid() {
  return [s4(), s4(), '-' , s4(), '-', s4(), '-', s4(), '-', s4(), s4(), s4()].join('');
}
function randomFromInterval(from,to){
    return Math.floor(Math.random()*(to-from+1)+from);
}
function get_random_color() {
    var letters = '0123456789ABCDEF'.split('');
    var color = '#';
    for (var i = 0; i < 6; i++ ) {
        color += letters[Math.round(Math.random() * 15)];
    }
    return color;
}
var data = new Array(500), types = ["date", "slider", "select", "string", "number", "rating", "level", "title"],
    allowModify = [true, false], str = "Cell";
for(var i = 0; i < 500; i++){
    var arr = new Array(100);
    for(var j = 0; j < 100; j++){
        var obj = {};
        obj.id = guid();
        obj.role = types[randomFromInterval(0, 6)];
        obj.selected = "";
        obj.writable = allowModify[randomFromInterval(0, 1)];
        switch(obj.role){
            case "slider":
                obj.range = [0, randomFromInterval(0, 100)];
                obj.text = 0;
                break;
            case "select":
                var num = randomFromInterval(2, 4), _options = Array(num);
                for(var opt = 0; opt < num; opt += 1 ){
                    _options[opt] = {
                        id : guid(),
                        text : ["Option[", opt + 1, "]"].join('')
                    }
                }
                obj.options = _options;
                obj.selected = _options[randomFromInterval(0, num - 1)];
                obj.text = obj.selected.text;
                obj.selected = obj.selected.id;
                break;
            case "date":
                obj.text = [randomFromInterval(2000, 2013), randomFromInterval(1, 12), randomFromInterval(1, 25)].join('/');
                break;
            case "string":
                obj.text = [str, "[", i , "][", j, "]"].join('');
                break;
            case "number":
                obj.text = randomFromInterval(1, 176432);
                break;
            case "rating":
                var _arr = [], colors = randomFromInterval(0, num - 1);
                for(var i = 0; i < colors; i++){
                    _arr[i] = get_random_color();
                }
                obj.colors = _arr;
                obj.text = _arr[1];
                break;
            case "level":
                obj.text = randomFromInterval(0, 100);
                obj.valid = {
                    "0-40" : get_random_color(),
                    "40-50" : get_random_color(),
                    "50-100" : get_random_color()
                }
                break;
        }
        arr[j] = obj;
    }
    data[i] = arr;
}
console.log(data);

You sure its infinite? Those two massive for loops plus a switch statement inside could cause some slow performance. — tymeJV
– tymeJV, Commented Oct 2, 2013 at 19:48
Get a copy of Firebug and step through the code in the debugger. It's a far more efficient method of debugging than asking SO contributors to guess where the error is. — user1864610
– user1864610, Commented Oct 2, 2013 at 19:50
@MikeW I have debugged the code and when I am going step by step there is no problem for first 3-4 iterations. But after that it is getting struck. Even for 100 loops, in the question I have mentioned 500. — Exception
– Exception, Commented Oct 2, 2013 at 19:51

Simon Fischer · Accepted Answer · 2013-10-02 19:50:09Z

3

You are using i two times in the loop, the first one in the outer loop and the second one in the loop under "rating", wich sets i to the number of colors, which I think is less than 500.

So if there is an object with the role "rating" in the first few objects, i will never reach 500 and thus ending in an infinite loop.

answered Oct 2, 2013 at 19:50

Simon Fischer

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Comments

Bemmu · Accepted Answer · 2013-10-02 19:51:36Z

2

You have this inner loop:

for(var i = 0; i < colors; i++){
    arr[i] = get_random_color();
}

It resets the value of i, messing up the outer loop. You can fix this by choosing another name instead of i here.

answered Oct 2, 2013 at 19:51

Bemmu

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1 Comment

Exception Over a year ago

Nice catch :), dumb mistake from my end.

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