Why can't I pass "window.location.reload" as an argument to setTimeout?

I would love some insight into the error I am seeing in Safari and Chrome with the following line of code:

setTimeout(window.location.reload, 250);

Chrome reports:
Uncaught TypeError: Illegal invocation

And Safari:
TypeError: Type error

In FireFox, the code runs fine. Also, this code runs fine in each of the three browsers:

setTimeout((function() {
  window.location.reload();
}), 250);

Chrome and Safari have no issues with this code:

var say_hello = function () { alert("hello") };  
setTimeout(say_hello, 250);  

What is special about window.location.reload that causes this error?

(not sure if it's useful or not, but here's a jsfiddle illustrating this)

Because reload() needs window.location as this. In other words - it is a method of window.location. When you say:

var fun = window.location.reload;

fun();

You are calling reload() function without any this reference (or with implicit window reference).

This should work:

setTimeout(window.location.reload.bind(window.location), 250);

The window.location.reload.bind(window.location) part means: take window.location.reload function and return a function that, when called, will use window.location as this reference inside reload().

See also

• https://stackoverflow.com/questions/10572673

• https://stackoverflow.com/questions/9639167

• https://stackoverflow.com/questions/8100469

There is another way of doing this, pretty simple, and no need of doing extra steps, bindings or stuff like that. When you use arrow functions instead of common functions in JS, the this context is included. So you could just as easily do the following:

setTimeout(() => window.location.reload(), 250);

Because this must be bound to location when you call reload. It's same as trying:

var reload = window.location.reload;
reload();

this would be window in non-strict mode and undefined in strict mode which are both invalid.

in non-old browsers you can do instead:

reload.call( location )

or in your example:

setTimeout( window.location.reload.bind( window.location ), 1000 )

Older IEs don't support explicit binding on host objects though.

You also get this for some native methods which are not generic such as:

var a = function(){}.toString;
a();
TypeError: Function.prototype.toString is not generic

Some are generic:

var fakeArray = {0:1,1:2,length:2};
fakeArray.join = [].join;
fakeArray.join( " " );
"1 2"

This fails because you're missing the location context (the function's this), when passing it your way. You would have to bind the context, before you can use it like this, for example with the underscore.js bind method

var boundReload = _.bind(window.location.reload, window.location);
setTimeout(boundReload, 500)

It's the same with any other function that is usually called from it's containing object like console.log