How to pass object's method as a parameter in Javascript

Question

Can't figure out how to pass object's method as a parameter properly.

Here is my code:

var MyTest = function (p1) {
  this.p1 = p1;
};
MyTest.prototype.getParam = function () {
  return this.p1;
};

function doAction(getParamCallback) {
  console.log(getParamCallback());
}

var mt = new MyTest(123);
console.log(mt.getParam()); // 123
doAction(mt.getParam);      // undefined

The only way to pass a method correctly I have found is to pass both object and method and use call():

function doAction2(obj, getParamCallback) {
  console.log(getParamCallback.call(obj));
}
doAction2(mt, mt.getParam);    // 123

Is there any way that requires only method to be passed, not both method and object?

Community · Accepted Answer · 2020-06-20 09:12:55Z

13

You need to pass the this context as well. In provided example, methos is being called in the context of window, and window does not have property p1

Use .bind() to pass the context. bind returns a function that when later executed will have the correct context set for calling the original function. This way you can maintain context in async callbacks, and events.[Reference]

Try this:

var MyTest = function(p1) {
  this.p1 = p1;
};
MyTest.prototype.getParam = function() {
  return this.p1;
};

function doAction(getParamCallback) {
  alert(getParamCallback());
}

var mt = new MyTest(123);

doAction(mt.getParam.bind(mt));

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Dec 29, 2015 at 6:03

Rayon

36.6k5 gold badges54 silver badges78 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Sujay Phadke Over a year ago

Thanks Rayon! This works perfectly in Google Apps Script as well!

Collectives™ on Stack Overflow

How to pass object's method as a parameter in Javascript

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related