'hasOwnProperty' in javascript -


i use obj.hasownproperty judge whether object has property, when replaced obj[prop] !== undefined, not normal implementation, ask, why behind method can not use it?

object.hasownproperty(prop); object[prop] !== undefined;

obj[prop] !== undefined wrong 2 reasons:

  1. you can explicitly set property undefined, obj[prop] = undefined;. obj.hasownproperty(prop) return true in case.
  2. obj[prop] follow prototype chain, return property that's inherited. obj.hasownproperty(prop) returns true if property exists directly in object, returns false inherited properties.

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