CODEWITHSUNDEEP
javascriptmethodsprototype
DR01D
DR01D

Reputation: 1365

What can I use to test methods added to functions and methods added to the prototype?

Question: In the following code what can I use to see if I've added methods correctly or alternately what can I use to see how badly I screwed up?

In the following test code I add a method to a function and it works as expected.

"use strict";

function aircraft() {
    return aircraft.myPlane();
}

aircraft.myPlane = () => 'XB-42';

console.log(aircraft());

In the next test code I add a method to the function's prototype and it also works as expected.

"use strict";

function aircraft() {
    return aircraft.prototype.myPlane();
}

aircraft.prototype.myPlane = () => 'XB-42';

console.log(aircraft());

However in that last example I think I might have done something dumb but I'm not entirely sure. Did that add the .myplane() function directly to the main Function prototype for all functions in the entire program? Is there a way for me to check and see what I've actually done so I can test and compare my results?

Upvotes: 1

Views: 26

Answers (1)

CertainPerformance
CertainPerformance

Reputation: 370729

You need to distinguish between functions and classes (that use the function keyword). In the first example, you're simply adding properties to the function, not to an instantiation of a class (which is probably what you were trying to do).

In a function constructor, you should reference that particular instantiation with this, like the following:

function Aircraft() {
  // function constructor (doesn't do anything useful in either example)
}
const myAircraft = new Aircraft();
// assigns to this instantiation only:
myAircraft.myPlane = () => 'XB-42';
console.log(myAircraft.myPlane());

To assign to the prototype, do something like this:

function Aircraft() {
// function constructor (doesn't do anything useful in either example)
}
// applies to all Aircraft:
Aircraft.prototype.myPlane = () => 'XB-42';
const myAircraft = new Aircraft();
console.log(myAircraft.myPlane());

Upvotes: 1

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