How to determine whether a JS object has a certain attribute

Whether the JS object has a certain attribute

Two methods, but slightly different

1, in operator

var obj = {name:'jack'};
alert('name' in obj); // --> true
alert('toString' in obj); // --> true

It can be seen that whether it is name or toString on the prototype chain, it can be detected and returned true.

2. hasOwnProperty method

var obj = {name:'jack'};
obj.hasOwnProperty('name'); // --> true
obj.hasOwnProperty('toString'); // --> false

The properties inherited from the prototype chain cannot be detected by hasOwnProperty and return false.

It should be noted that although in can detect the properties of the prototype chain, for in usually cannot.

Of course, after rewriting the prototype, for in will be visible under IE9/Firefox/Safari/Chrome/Opera. See: Defects of for in

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