What is the use of the “this” keyword here?

Question

class Rabbit1 {
  constructor(name, color, type) {
    if (arguments.length !== 3) throw new Error("Wrong length of arguments given");
    this.ar1 = name;
    this.ar2 = color;
    this.ar3 = type;
    this.testExtra = [];
    if (!name) {
      this.testExtra[0] = "This is in the constructor";
    } else {
      this.testExtra[0] = "Name is True";
    }
  }
  speak(line) {
    console.log(`The ${this.ar2} Rabbit, called '${this.ar1}'  and says it\ 's a ${this.ar3} rabbit, Oh and it\'s saying ${line} too... ${this.testExtra}`);
  }
  speak2(speak) {
    console.log("Hello " + this.ar1);
  }
}

let blackR = new Rabbit1(false, "black", "gentle");

blackR.speak("Hello");

I’m asking this question because, if you take a look at

if (!name)

The binding name is used, and it refers to the name of the instance of the class (in this case blackR).

So why do you we use this.name when name on its own refers to the name value given in the instance of the class.

Please bear, with the poor indentation. Thanks.

Possible duplicate of [What does "this" mean?](https://stackoverflow.com/questions/4195970/what-does-this-mean) — Derviş Kayımbaşıoğlu, Dec 08 '18 at 09:56
You can use `this.ar1` or `name` in the constructor, because there (and only there) both exist. `name` is just the function's parameter (a local variable), while `this.ar1` has just been defined with the same value, and is a member of the object instance. — trincot, Dec 08 '18 at 09:59
"So why do you we use this.name when name on its own refers to the name value given in the instance of the class." -> `name` does refer to the name (huh), but it won't exist anymore at the end of the constructor's code. `this.name`, on the other hand, will remain within the returned object. — Jeto, Dec 08 '18 at 10:00
They are not the same binding. name by itself is the parameter of the constructor. They just happen to have the same value. Actually you should not make references to parameters because you risk capturing them and it could cause some weird effects unless you specifically intend to capture them. — Chris Rollins, Dec 08 '18 at 10:00
check this for typescript: https://github.com/Microsoft/TypeScript/wiki/'this'-in-TypeScript — Derviş Kayımbaşıoğlu, Dec 08 '18 at 10:03

score 0 · Accepted Answer · answered Dec 08 '18 at 12:50

The binding name is used, and it refers to the name of the instance of the class (in this case blackR).

No, it doesn't. name is the first parameter in the constructor:

constructor(name, color, type) {

The first value in the call is false:

let blackR = new Rabbit1(false, "black", "gentle");

So that is the value assigned to name. It's also assigned to this.ar1 in:

this.ar1 = name;

The code produces:

"The black Rabbit, called 'false'  and says..."

Which shows that this.ar1 has a value of false.

So why do you we use this.name when name on its own refers to the name value

The expression this.name does not appear in the OP. If you meant "Why is this.ar1 used instead of name", it's impossible to tell from the posted code. Within the constructor, they are essentially identical and have the same value.

However, ar1 is a public property of the instance, so can be changed later.

What is the use of the “this” keyword here?

1 Answers1