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JavaScript·Intermediate·Coding·1 min read

How does property lookup use the prototype chain?

Short interview answer

The engine first checks the object's own properties. If absent, it follows the object's internal [[Prototype]] link and repeats until it finds a property or reaches null. Accessor properties may execute a getter with the original receiver as this.

Example

JavaScript
const animal = { speak() { return 'generic'; } };const dog = Object.create(animal);dog.bark = () => 'woof';
dog.bark();  // 'woof'    — own propertydog.speak(); // 'generic' — found one level up on `animal`dog.fly;     // undefined — chain ends at Object.prototype -> null

Key takeaway

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

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