Cancel an infinite loop in JavaScript

Question

I am trying to timeout a function in case it has an infinite loop. But the below does not work. Any idea why and how to fix it?

setTimeout(clearValues,1000);

function clearValues(){
    i=0;
    alert("hi "+i);
}

i=19
function infin(){
    while(i>0){
        console.log(i);
        i++;
    }
    alert("Done");
}

infin();

In the below case, I get the alert displayed ( a bit later than expected ) and the console statements continue printing even after the alert. That means setTimeout did not wait for the loop to end in this case. Any explanation for this?

setTimeout(clearValues,500);

function clearValues(){
    alert("clear");
}


function infin(){
for(i=0;i<10000;){
    i=i+0.3;
    console.log(i);
}
}

infin();

On which action are u calling these functions??

AkshayJ
– AkshayJ

2015-06-29 06:09:21 +00:00
Commented Jun 29, 2015 at 6:09 — AkshayJ
– AkshayJ, Commented Jun 29, 2015 at 6:09
No specific action. This just runs as a script.

codingsplash
– codingsplash

2015-06-29 06:10:00 +00:00
Commented Jun 29, 2015 at 6:10 — codingsplash
– codingsplash, Commented Jun 29, 2015 at 6:10
the second example does work only after the loop finished.

Nina Scholz
– Nina Scholz

2015-06-29 06:40:41 +00:00
Commented Jun 29, 2015 at 6:40 — Nina Scholz
– Nina Scholz, Commented Jun 29, 2015 at 6:40

u.k · Accepted Answer · 2015-06-29 06:25:39Z

3

setTimeout works asynchronously, means it will run after 1000ms and the previous event loop is completed. Since the while loop will never be completed, the callback will never be called.

Add a condition to the loop if you want to exit it.

edited Jun 29, 2015 at 6:25

answered Jun 29, 2015 at 6:12

u.k

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1 Comment

u.k Over a year ago

It probably has to do with the implementation of console.log. if you'll test it in different browser you'll probably get different results.

Jean F. · Accepted Answer · 2015-06-29 06:15:55Z

1

Another solution might be to use interval:

var code = function(){ 
              console.log('tick'); 
           };
var clock = setInterval(code, 200);

When you don't need it anymore:

clearInterval(clock);

answered Jun 29, 2015 at 6:15

Jean F.

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4 Comments

Tushar Over a year ago

OP is using setTimeout and not setInterval

Jean F. Over a year ago

Sorry but what OP stands for?

Tushar Over a year ago

It is the person who asks the question

codingsplash Over a year ago

@JeanF. OP - Original Poster

Nina Scholz · Accepted Answer · 2015-06-29 08:16:39Z

It works, when you made the infin call with a slightly different change.

var i = 0;
setTimeout(clearValues, 1000);
var interval = setInterval(infin, 0);

function clearValues() {
    out("clear");
    clearInterval(interval);
}

function infin() {
    if (i < 10000) {                    // if you be shure that you
        i++;
        out(i);
    } else {                            // never reach the limit,
         clearInterval(interval);       // you can remove the four
    }                                   // commented lines
}

function out(s, pre) {
    var descriptionNode = document.createElement('div');
    if (pre) {
        var preNode = document.createElement('pre');
        preNode.innerHTML = s + '<br>';
        descriptionNode.appendChild(preNode);
    } else {
        descriptionNode.innerHTML = s + '<br>';
    }
    document.getElementById('out').appendChild(descriptionNode);
}

<div id="out"></div>

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