通过变量传递函数

Question

I've this situation:

<script>
var cb;
function doSomething(c) {
    cb = c();
}

cb();
</script>

But it doesn't work. I want to set a variable as function, to make a callback called by other functions.. Some ideas?

Answer 1

c() executes the function and returns a value, you need to pass a reference to it:

cb = c

Also, you should call the function doSomething(func) to make the assignment.

doSomething(function(){ alert('hello'); });
cb(); // "Hello"

But if what you want is a callback then you don't need a global variable:

function doSomething(callback) {
  // do something
  if (callback) callback();
}

When you run the function with another function as parameter the callback will run.

Answer 2

You need to assign cb first with your function:

<script>
var cb;
function doSomething(c) {
    cb = c;
}

var myFunc = function(){
   window.alert("test");
}

doSomething(myFunc);

cb();
</script>

And if you do cb=c(); you will execute function c instantly and return the value to cb if you want the variable cb as the result of c , do like this. otherwise, assign without running it.

Answer 3

You have 3 options to set a variable to a functiion

1. var fn = functionname;
2. var fn = function(param){}; this will be an anonymous function
3. var fn = function FunctionName(param){}; this will be a named function, comes in handy when debugging, since it will present you with a function name ( console.log(c);

You cann call it like var returnVal = fn(); or pass it to a function var returnVal = myFunc(fn); where myFunc calls the param, let it be inFn it like inFn();

What might be interesting to note: Since such a function is related to the global context, you can bind an object to it alter its scope. That gives you the possibility of this referencing the bound object. (Be aware, bind is not supported by all browsers as it is defined ECMAScript 5 , but there are quite some polyfills out there.)

• fn.bind(object);

Or call it in another context with fn.call(object, param1, param2) or fn.apply(object, [param1, param2]) . Nice write up on this Link to odetocode.com/blog .