Question

I have a function in javascript:

function test(){
...
    if (){
        setTimeout(test(), 1000);
    }
}

according to the manual, i can call this with:

setTimeout(test(), 1000);

in fact, it calls, but do not wait the 1s. so I try to use it like the following and it works.

setTimeout(function(){test();}, 1000);  

Anyone can explain this to me?

Answer 1

You should be calling with

setTimeout(test, 1000);

and NOT with

setTimeout(test(), 1000);

In other words, the function you want to call after 1000 ms is test, not the result of calling test!

The reason why

setTimeout(function(){test();}, 1000);  

works is that the function you call after 1000ms is a function that calls test, which is basically test itself. For lambda calculus geeks, that’s called eta-reduction.