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Discussion on: Write faster JavaScript

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javaguirre profile image
Javier Aguirre •

Thank you for the article, insightful. :-)

I didn’t get very well your explanation about arrow functions, although your point is don’t use it inside a class cause it has no scope and it will be recreated every time, right?

Thank you!

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yashints profile image
Yaser Adel Mehraban •

Apart from recreation of the function itself it has other drawbacks too.

Let me give you two examples, first let's say you have a class with an arrow function and when testing you want to mock it:

class A {
  static color = "red";
  counter = 0;

  handleClick = () => {
    this.counter++;
  }

  handleLongClick() {
    this.counter++;
  }
}

Usually the easiest and proper way to do so is with the prototype as all changes to the Object prototype object are seen by all objects through prototype chaining.

But in this instance:

A.prototype.handleLongClick is defined.

A.prototype.handleClick is not a function.

Same happens with inheritance:

class B extends A {
  handleClick = () => {
    super.handleClick();

    console.log("B.handleClick");
  }

  handleLongClick() {
    super.handleLongClick();

    console.log("B.handleLongClick");
  }
}

Then:

new B().handleClick();
// Uncaught TypeError: (intermediate value).handleClick is not a function

new B().handleLongClick();
// A.handleLongClick
// B.handleLongClick