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In JavaScript, prototypal inheritance is implemented through the prototype chain, where objects delegate property lookups to their internal [[Prototype]] link. Understanding the difference between prototype, __proto__, and the chain itself is key to mastering object behavior.
Prototype Chain Every object has an internal [[Prototype]] (accessible via Object.getPrototypeOf(obj) or the non-standard __proto__). When you access a property, JavaScript:
Checks the object’s own properties.
If not found, follows [[Prototype]] to the next object.
Continues until the property is found or null is reached. This lookup mechanism is the prototype chain.
__proto__
Exists on all objects (except those with null prototype).
Points to the object’s [[Prototype]].
Can be used to read or set the prototype, but is deprecated in favor of Object.getPrototypeOf / Object.setPrototypeOf.
Example:
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