How to pass parameters in eval in an object form?

Question

I have this json, and when i get this json i need to run the function which comes at callback object.

{
  formId: 'snn_service_item_form',
  item_id: '1',
  item_title: 'some item',
  item_description: '',
  item_duration: '10',
  item_price: '120',
  item_level_1: 1,
  item_level_2: 0,
  item_level_3: 1,
  item_type: 'p',
  callback: {
    callbackName: 'getServices',
    callbackParams: {
      _param1: 1,
      _param2: 2
    }
  }
}

so according to this i need to run this:

getServices(1,2);

i can do that with eval function like:

eval(json.callback.callbackName+'(\''+ json.callback.callbackNParams._param1 +'\',\''+ json.callback.callbackNParams._param2 +'\')');

i can automate this by putting it into a for in and writing parameters to a string, but i dont think this is the best way to go.

is there a way to assign function name from a var and giving its parameters as an object, in my case like:

json.callback.callbackName(json.callback.callbackParams);

i know this is not the way to do it but it is what i want to learn.

Thanks, Sinan.

Solution 1

Depends on where the function to call is defined (global scope or a local scope).

If global, you don't need eval (and it's safer to avoid it), you just reference the function through the global window object:

var args = [];
for(var p in json.callback.callbackParams) {
    args.push(json.callback.callbackParams[p]);
}
window[json.callback.callbackName].apply(null, args)

See the apply() function used above.

If it's in a local scope, then you need the eval (how you have it is fine).

Solution 2

Don't use eval. You can get a reference to a named global variable or function from the window object:

var callbackfunction= window[json.callback.callbackName];

And trying to serialise your values to a string just to have them parsed back to JavaScript unreliably is silly. Call the function explicitly:

callbackfunction.call(window, json.callback.callbackParams.param1, json.callback.callbackParams.param2);

(window here is a dummy value for this for when you're not using object methods.)

Better for automating it to accept any number of parameters would be to turn callbackParams into a plain Array:

callbackParams: [1, 2]

and then use apply to call the function:

callbackfunction.apply(window, json.callback.callbackParams);

Comments

[Amit Patil]

For a local scope, you could use the eval just to get the function object, and then still use the more-reliable apply to call it. BTW it's not guaranteed that for(in) will return the params in the order you want.

[kangax]

func.call(null, ...) will give you the same (well, almost) behavior as func.call(window, ...) — invoking function with this value being global object. It's shorter, although probably less descriptive for beginners.