如何在没有括号的情况下调用函数时传递参数[Javascript]

Question

I have a function called "tryMe" and I'm calling it without the parenthesis not precisely this but the idea is like what you would do here:

setTimeout(tryMe,200);

how can I pass parameters that I need?

I am using a jquery plugin that enables me to call a function but I have to call it withou the parenthesis or it executes itself upon loading.

Answer 1

setTimeout(function() { tryMe(parm1, parm2); }, 200);

A more robust offering, to ensure that the values of parm1 , parm2 don't change before the timeout fires (per @lincolnk's comment):

 
 
 
  
  setTimeout(function() { var p1 = parm1; var p2 = parm2; tryMe(p1, p2); }, 200);
 
  

@patrick dw, you're right, has to be evaluated before.

Answer 2

You can wrap tryMe in a closure.

For example:

var f = function(){tryMe('some parameter');};
setTimeout(f, 200);

Here, we create a function object, f , which calls tryMe with the desired parameter(s). Then we pass f to setTimeout . When the timeout expires, f will be called, which will in turn call tryMe with the desired parameters.

A word of warning if you wish to pass in parameters that may change before the timeout gets called (for example, if you are setting several timeouts in a for loop): you will want to bind those variables like so:

var f = function(someParamter){return function(){tryMe(someParameter);};};
setTimeout(f(someParameter), 200);

The reason simply doing something like

setTimeout(tryMe('some parameter'), 200); //Does not work.

doesn't work is because you are passing the result of evaluating tryMe instead of the function object tryMe itself.

Answer 3

You are not calling the function, the browser does - after 200 milliseconds. You are merely providing it with the function that needs being called. Firefox actually allows specifying additional parameters in the setTimeout call:

setTimeout(tryMe, 200, "first parameter", "second parameter");

However, as far as I know no other browsers support this feature so you should really use a closure function as explained by other answers already. Here you create a temporary function with the sole purpose of calling your original function with the right parameters.

setTimeout(function() {tryMe("first parameter", "second parameter")}, 200);