setInterval javascript - how to call function

Question

Here is the simple example of two similar use of setInterval function:

In the first example setInterval function does not work, in the second version where below syntax was used it's working fine.

/* This part does not work */
var i = 0;
function displayNumber() {
  i++;
  $('#result').html(i);
}

setInterval(displayNumber(), 500);

/* This part does work */
var j = 0;
function displayNumberOk() {
  j++;
  $('#result-ok').html(j);
}

setInterval(function() { displayNumberOk() }, 500);

In specification I can find:

setInterval(function,milliseconds,param1,param2,...)

Why can't I use function name directly?

Why are you posting the working version of your code here and not the broken version? Don't make people visit links to discover what the problem is. — user1106925
– user1106925, Commented Apr 27, 2015 at 15:31

Matteo Tassinari · Accepted Answer · 2015-04-27 15:29:48Z

6

In the first example, where you have

setInterval(displayNumber(), 500);

you are calling displayNumber directly, instead of passing it as parameter.

In fact, using

setInterval(displayNumber, 500);

should be sufficient (notice the lack of (), so that it is not called but rather passed as parameter).

answered Apr 27, 2015 at 15:29

Matteo Tassinari

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