Prototype chains, prototypal inheritance, and how the this keyword is bound in different contexts, each explained with a short example.
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- What is a prototype in JavaScript?
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An object that serves as a template for other objects, containing properties and methods that can be inherited by instances.- How do you access an object's internal prototype?
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Using Object.getPrototypeOf(obj) or the legacy __proto__ property. Modern code prefers Object.getPrototypeOf().- What is the difference between obj.__proto__ and Function.prototype?
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__proto__ is an instance's link to its prototype, while Function.prototype is a property on a constructor function that becomes the __proto__ of new instances.- What is the prototype chain?
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A series of linked prototypes where an object inherits properties from its prototype, which itself has a prototype, forming a chain that eventually ends at null.- How does property lookup work in the prototype chain?
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JavaScript first checks the object itself; if not found, it checks the object's prototype, then the prototype's prototype, continuing until the property is found or null is reached.- What does Object.getPrototypeOf(obj) return?
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The internal prototype of obj, equivalent to obj.__proto__ but using the standard recommended approach.- What is a constructor function?
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A regular function intended to be called with the `new` keyword to create and initialize objects; by convention, constructor names are capitalized.- What does the `new` keyword do?
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Creates a new empty object, sets the object's __proto__ to the constructor's prototype property, calls the constructor with `this` bound to the new object, and returns the object.- Why should methods be defined on the prototype rather than in the constructor?
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Methods on the prototype are shared by all instances, saving memory; methods in the constructor create a new copy for each instance.- How do you set up prototypal inheritance?
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Assign the parent's prototype to the child constructor's prototype using Object.create(), then reassign the constructor property to point back to the child.- What is Object.create(proto)?
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Creates a new object with its internal prototype set to the proto argument, optionally adding properties via a descriptor map.- What is `this` in JavaScript?
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A special keyword that refers to the object on which a method is being called; its value depends on how the function is invoked.- What does `this` refer to in a regular function called without an object?
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In non-strict mode, `this` refers to the global object (window or global); in strict mode, `this` is undefined.- What does `this` refer to when a method is called on an object?
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`this` refers to the object the method is called on (the object before the dot in object.method()).- What does `this` refer to in a constructor called with `new`?
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`this` refers to the newly created object that the constructor is initializing.
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