So If i am doing:

setInterval(function(){

   console.log("1");

},Infinity);

It keeps on logging 1 as if it is a for loop. Why is that behaviour?

So If i am doing:

setInterval(function(){

   console.log("1");

},Infinity);

It keeps on logging 1 as if it is a for loop. Why is that behaviour?

• javascript

• 2 1) Because setInterval essentially is a for loop. 2) Because the parison to determine whether it's time for the next iteration likely arrives at the answer yes at any time using a parison to Infinity. – Since this code is rather nonsensical, I wouldn't expect any particular "right" answer here anyway. – deceze ♦ Commented Dec 18, 2015 at 8:03
• @deceze What I think is the output is nonsensical. – void Commented Dec 18, 2015 at 8:07
• 1 Garbage in, garbage out. :) – deceze ♦ Commented Dec 18, 2015 at 8:11
• @deceze hehe yeah, right! – void Commented Dec 18, 2015 at 8:11

3 Answers 3

When the float/number Infinity needs to be converted to a 32-bit integer value in JavaScript, as it does for setTimeout, it's converted to zero:

console.log(typeof Infinity); // number
console.log(Infinity | 0);    // 0

ECMA-262 6e Section 7.1.5 ToInt32 ( argument )

The abstract operation ToInt32 converts argument to one of 2³² integer values in the range −2³¹ through 2³¹−1, inclusive. This abstract operation functions as follows:

1. Let number be ToNumber(argument).
2. ReturnIfAbrupt(number).
3. If number is NaN, +0, −0, +∞, or −∞, return +0.
4. [...]

Infinity only has use in arithmetics, and its behaviour is therefore only defined in arithmetics. In any other context it's just an object with some properties:

The value of Infinity is +∞ (see 6.1.6). This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

As this object has no use as the delay parameter of setTimeout that function executes as if no object was supplied, so 0.

My closest guess is that the interval argument you specify in setInterval is subjected to division when pared with the time counters to determine if the next iteration should be done. The function must be called without an interval since it is zero when any number is divided by Infinity.

if (counter / Infinity === 0)
   callback();

In the above code, callback() will execute for any counter.