CODEWITHSUNDEEP
javascriptconstructorsingletoninstanceof
DoryuX
DoryuX

Reputation: 179

Why does instanceof return false for a singleton using a constructor with arguments?

I'm trying to check for a specific type of object in my code. Even though the object has the constructor in its prototype, it is still failing to return the correct object type and always returns with "object" when using the instanceof operator.

Here's an example of the object:

Simple = (function(x, y, z) {
    var _w = 0.0;

    return {
        constructor: Simple,

        x: x || 0.0,
        y: y || 0.0,
        z: z || 0.0,

        Test: function () {
            this.x += 1.0;
            this.y += 1.0;
            this.z += 1.0;

            console.log("Private: " + _w);
            console.log("xyz: [" + this.x + ", " + this.y + ", " + this.z + "]");
        }
    }
});

Upvotes: 0

Views: 303

Answers (1)

Digital Plane
Digital Plane

Reputation: 38274

You're returning an object literal with the constructor property to set to the function Simple. The internal constructor is still set to Object, so instanceof returns false.
For instanceof to return true, you need to set properties using this.property in the constructor or use prototypes, and initalize a new object using new Simple().

function Simple(x, y, z) {
    var _w = 0.0;

    this.x = x || 0.0;
    this.y = y || 0.0;
    this.z = z || 0.0;

    this.Test = function () {
            this.x += 1.0;
            this.y += 1.0;
            this.z += 1.0;

            console.log("Private: " + _w);
            console.log("xyz: [" + this.x + ", " + this.y + ", " + this.z + "]");
        }
  });
  (new Simple()) instanceof Simple //true

Upvotes: 1

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