Difference between prop in obj and obj.hasOwnProperty (prop) and obj [prop]?

Question

Should I use one over the other? Does everyone use them better together? Thanks.

Answer 1

• prop in obj checks to see if the obj property has a property named prop , even if it is just inherited from the prototype.

• obj.hasOwnProperty(prop) checks to see if obj itself has a property named prop ; it ignores properties inherited from prototypes.

• obj[prop] gets the value of the prop property.

Use what is appropriate for what you are trying to accomplish

Note. In all three cases, prop must be a string.

Answer 2

Just for an example:

 var animal = {"legs": 4}; var dog = {"barks" : true}; dog.__proto__ = animal; // JS inheritance (dog inherits from animal) 

now it means that:

 console.log("legs" in dog); // TRUE - due to JS inheritance and since 'in' key looks into inherited prototypes console.log(dog.hasOwnProperty("legs")); // FALSE console.log(dog.hasOwnProperty("barks")); //TRUE 

prints

 true false true 

Note one more thing: if the dog had the “legs” property, let's say 5 (hhmm spooky, which I know), so the “in” operator (“legs” of the dog) will refer to the “legs” property that is declared in the dog’s subject rather than inherited “legs” that come from an animal’s object. eg:.

 var animal = {"legs": 4}; var dog1 = {"barks": true}; var dog2 = {"barks": true, "legs": 5}; dog1.__proto__ = animal; dog2.__proto__ = animal; console.log(dog1.legs); console.log(dog2.legs); console.log("legs" in dog2) // 'in' refer to the un-inherited "legs" of dog2 

prints

 4 5 true