JS: Using variable names to call function.

Question

Im working with jQuery. I have an app that makes ajax requests to server that responds with JSON.

in some cases the response from the server will indicate the name of a JS function to be called

{"responseType":"callback", "callback":"STUFF.TestCallback","callbackData":"this is in the callback"}

If the responseType is "callback" as above the JSON is passed to a function to handle this response type. (the var "response" contains the JSON above)

STUFF.callback = function(response){
    if(typeof response.callback =='function'){
        console.log("All Good")
        response.callback(response);
    }else{
        console.log("Hmm... Cant find function",response.callback );
    }
}


STUFF.TestCallBack = function(data){
    alert("it worked"); 
}

But when I do this I get the error "response.callback is not a function".

Any comments on why this is not working and how to do this properly would be greatly appreciated.

Answer 1

A String is a String, not a Function.

response.callback() doesn't work because it is the same as "STUFF.TestCallback"() not STUFF.TestCallback()

You probably want to have the data structured something more like "callback": "TestCallback" then then do:

STUFF[response.callback](response);

Here you use the String to access a property of STUFF. (foo.bar and foo['bar'] being equivalent.)

Answer 2

You propably could do

var myfunction = eval(response.callback);
myfunction(response);

although using eval() is considered as a bad style by some javascript developers.

Answer 3

You could transform that "namespace.func" into a call like this:

STUFF.callback = function(response) {
  var fn = response.callback.split("."), func = window;
  while(func && fn.length) { func = func[fn.shift()]; }
  if(typeof func == 'function') {
    console.log("All Good")
    func(response);
  } else{
    console.log("Hmm... Cant find function", response.callback);
  }
}

What this does it grab the function by getting window["STUFF"] then window["STUFF"]["TestCallback"] as it loops, checking if each level is defined as it goes to prevent error. Note that this works for any level function as well, for example "STUFF.One.Two.func" will work as well.