Defining Javascript Getter And Setter Functions

Defining a function inside object:

let o = {
    a() {
        return 42;
    }
};

console.log(o);
console.log(o.a);
console.log(o.a());

Output:

From above we can see a() is an ordinary function.

Now rewriting a() as a getter function:

// -----------------------

let o2 = {
    get a() {
        return 42;
    }
};

console.log(o2);
console.log(o2.a);
// console.log(o2.a()); // Uncaught TypeError: o2.a is not a function

In above code the a() is defined with get so it’s a getter function. Here’s the output of the code:

Above is the getter function. To define a setter function, here is the example:

let o3 = {
    v: 0,
    set a(x) {
        this.v = x;
    }
};

console.log(o3);
o3.a = 42;
console.log(o3.v);

In above we define a function a() and prefixed it with set, and then we can set the value of v by o3.a = 42.

Here is the output of the code:

Finally here is the code showing how to add getter and setter functions by the Object.defineProperties() function:

// ------------------------

let o4 = {
    v: 0
};

Object.defineProperties(o4, {
    'g': {
        get: function () {
            return this.v;
        }
    },
    's': {
        set: function (x) {
            this.v = x;
        }
    }
});

console.log(o4.g);
o4.s = 42;
console.log(o4.g);

Here is the output of the above code:

References

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