Created
May 5, 2013 14:43
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hasOwnProperty() example
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| function rightWay(obj) { | |
| for (var key in obj) { | |
| // Ignore properties that are inherited. | |
| if (!obj.hasOwnProperty(key)) { | |
| continue; | |
| } | |
| console.log(key); | |
| } | |
| } | |
| function wrongWay(obj) { | |
| for (var key in obj) { | |
| console.log(key); | |
| } | |
| } | |
| // You start out with code like this. | |
| var obj = {}; | |
| obj.x = 1; | |
| obj.y = 2; | |
| wrongWay(obj); | |
| // .. which logs `x` and `y`. | |
| // Then one day you use a new library that extends | |
| // a base prototype without making the new property non-enumerable. | |
| Object.prototype.answer = 42; | |
| // Suddenly your code breaks because it is including the new property | |
| // that it didn't expect. | |
| wrongWay(obj); | |
| // .. now logs `x`, `y`, and `answer` (from the prototype). | |
| // You could have protected yourself by using | |
| // `hasOwnProperty()` to ensure you only iterated | |
| // over the properties on the object itself. | |
| rightWay(obj); | |
| // .. logs `x` and `y`, ignoring `answer` because it is on the prototype. | |
| // Also the library author could have made `answer` non-enumerable | |
| // to help avoid this problem but using `hasOwnProperty()` | |
| // is still best-practice unless you /want/ to include | |
| // the prototype's properties, of course. |
This is awesome explanation. To the point. Thanks 👍
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thanks for the simple explanation