Enhancing TypeScript modules - accessing the instance reference

Question

Enhancing TypeScript modules - accessing the instance reference

While I have a good understanding of how module augmentation works, I am struggling to obtain the object reference in the new method's implementation.

To provide an example, I aim to enhance the es2015 Map interface.

In my code, I include:

declare global{
    interface Map<K, V> {
        newMethod(g: K): V;
    }
}

This setup appears to be functioning correctly as I can observe the new method in my other code.

However, when attempting to implement this new method, I am uncertain of how to access a reference on the Map instance to make further calls to other methods like `get` or `keys`.

I experimented with the following approach:

Map.prototype.newMethod = k => {
   ...
   let leys = this.keys();
   ...
}

Unfortunately, this solution does not work as expected.

Could you please advise me on how to tackle this issue?

typescript

Answer 1

Answer №1

Arrow functions cannot be used when adding methods to a prototype object.
Consider the following code snippet:

Map.prototype.newMethod = k => {
   let leys = this.keys();
}

After compilation, it transforms into:

var _this = this;
Map.prototype.newMethod = function (k) {
    var leys = _this.keys();
};

However, _this does not reference the correct instance.
Even if you transpile it to ES6 while keeping the arrow function, the behavior remains the same due to the nature of arrow functions.

The proper approach is as follows:

Map.prototype.newMethod = function(k) {
   ...
   let keys = this.keys();
   ...
}

Answer 2

Arrow functions cannot be used when adding methods to a prototype object.
Consider the following code snippet:

Map.prototype.newMethod = k => {
   let leys = this.keys();
}

After compilation, it transforms into:

var _this = this;
Map.prototype.newMethod = function (k) {
    var leys = _this.keys();
};

However, _this does not reference the correct instance.
Even if you transpile it to ES6 while keeping the arrow function, the behavior remains the same due to the nature of arrow functions.

The proper approach is as follows:

Map.prototype.newMethod = function(k) {
   ...
   let keys = this.keys();
   ...
}

Answer 3

Answer №2

Opt for traditional functions instead of arrow functions.

Map.prototype.newMethod = function newMethod() {
  let leys = this.keys();
};

It's important to make a deliberate decision when choosing between arrow functions and normal functions rather than just following the trend of using arrow functions.

One key difference is that arrow functions do not have bindings for this or arguments; instead, they are bound to the closest lexical scope.

Answer 4

Opt for traditional functions instead of arrow functions.

Map.prototype.newMethod = function newMethod() {
  let leys = this.keys();
};

It's important to make a deliberate decision when choosing between arrow functions and normal functions rather than just following the trend of using arrow functions.

One key difference is that arrow functions do not have bindings for this or arguments; instead, they are bound to the closest lexical scope.

Enhancing TypeScript modules - accessing the instance reference

Answer №1

Answer №2

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