Difference between Javascript property with and without underscore

vaichidrewar
July 6, 2023
221 views
0 votes
2 Answers

I saw the below code at https://javascript.info/class

Its constructor is taking the name parameter and assigning it to this.name. Then in the getter named name it is returning this._name. Why does this code work even when the constructor is not using this._name to set the value?

class User {

  constructor(name) {
    // invokes the setter
    this.name = name;
  }

  get name() {
    return this._name;
  }

  set name(value) {
    if (value.length < 4) {
      alert("Name is too short.");
      return;
    }
    this._name = value;
  }

}

let user = new User("John");
alert(user.name); // John

user = new User(""); // Name is too short.

Tags: javascript

Answers

- jabaa
- July 6, 2023 at 2:32 am
- 0 votes
0
The underscore is a normal character and doesn’t have a special meaning in JavaScript. You could replace it with p for private or something else.

The property this.name has a getter and a setter.

this.name = name; in the constructor calls the setter. There is even a comment // invokes the setter.

The setter set name(value) sets this._name = value;.

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- symlink
- July 6, 2023 at 2:48 am
- 0 votes
0
The get and set keywords mean those funcs are invoked automagically, so when you create the new User and call alert(user.name), you’re accessing _name and never name. You could rename _name to foo or _foo and it would work the same way.
```
...
  get name() {
    return this.foo;
  }

  set name(value) {
    ...
    this.foo = value;
  }

}

let user = new User("John");
alert(user.name); // John (still works)
```
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