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JavaScript·Intermediate·Coding·1 min read

How are constructor.prototype and an instance's prototype related?

Short interview answer

When a constructable function is called with new, the new object's [[Prototype]] is normally set to the constructor's prototype property. The prototype property itself is just an ordinary property on the constructor function; it is not the constructor's own prototype.

Example

JavaScript
function Point(x) { this.x = x; }Point.prototype.describe = function () { return `x=${this.x}`; };
const p = new Point(3);Object.getPrototypeOf(p) === Point.prototype; // truep.describe();                                 // "x=3" (via the chain)

Key takeaway

Explain the underlying mental model clearly, then support it with a concrete example and its trade-offs.

← Back to Prototype chain

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