What is a prototype in JavaScript?

Q: What is a prototype in JavaScript?

Every object has a property called `[[Prototype]]`. This property references another object, known as the object's prototype. When an object is created, its `[[Prototype]]` property is set to the prototype of its constructor function. The prototype of an object points to another object or to null — Properties of the object's [[Prototype]] can also be accessed on the object itself.

Difficulty: 5/10

prototype chain, inheritance, object creation

A prototype in JavaScript is an object that acts as a blueprint for other objects. Objects can inherit properties and methods from their prototypes, creating a prototype chain. An object can be used as a prototype to create a new object.

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Every object has a property called [[Prototype]]. This property references another object, known as the object's prototype. When an object is created, its [[Prototype]] property is set to the prototype of its constructor function.
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The prototype of an object points to another object or to null —
3
Properties of the object's [[Prototype]] can also be accessed on the object itself.

Scenario Questions

0-2 years experience

2-5 years experience

1You notice that a new property added to `Array.prototype` is causing unexpected behavior in a third‑party library. How would you debug and resolve the issue?

Follow-up Questions