Recommended method to determine whether 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

You can see that whether it is name or toString on the original chain, it can detect the return true.

2. HasOwnProperty method

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

The inherited properties on the prototype chain cannot be detected by hasOwnProperty, returning false.

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

Of course, after rewriting the prototype for in is visible under IE9/Firefox/Safari/Chrome/Opera.

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