How to get the obj the method is called upon from inside a callback function?

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,
#1

I call a method on an object. And the method takes a callback function as a parameter. As:

obj.method(callbackFn);

Inside the callback function, I want to work with the object the method is called upon. I want to declare the callback function and save it to a global variable since I may use this callback later in multiple methods upon multiple objects. As:

const predeclaredFunc = () => { 
 //func body needs to work with the obj that calls the method which has this predeclared func as callback argument
};
const obj1 = {
  methodA(callbackFn){callbackFn()};
};
const obj2 = {
  methodB(callbackFn){callbackFn()};
};

obj1.methodA(predeclaredFunc); // predeclaredFunc will work with obj1
obj2.methodB(predeclaredFunc); // predeclaredFunc will work with obj2

So I have to use something like the this keyword to refer to the object in the callback function body, instead of using its name. But I dont know how to.

For example, with the array.forEach method, say I want the callback to console log the array for each element of the array.
I will want to have something like this (not working):

const arr = [0, 1, 2]; //any random array with length 3

/ I want the callback to console log the array 3 times
const callback = () => {
console.log(this);
}
//does using arrow function in this case make difference from using func declaration/expression?

arr.forEach(callback); 
//not working. it's logging ' {} {} {} ' to the console

Help Please! Many thanks!

#2

Try something like this:

const array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

const obj = {
    a: [5, 7, 9],
    b: function() {
        console.log(this)
    }
}

obj.b.call(array)

Returns:

[
  1, 2, 3, 4,  5,
  6, 7, 8, 9, 10
]

But, to be honest, I just wouldn’t use forEach in that case. I’d just call logThis() or some similar function on the array itself instead of calling it from within a forEach, but it depends what you want to do.

Also, check this page out for clarifications on call, apply, and bind: