Hidden Features of JavaScript? [closed]

Answer 1

To properly remove a property from an object, you should delete the property instead of just setting it to undefined:

var obj = { prop1: 42, prop2: 43 };

obj.prop2 = undefined;

for (var key in obj) {
    ...

The property prop2 will still be part of the iteration. If you want to completely get rid of prop2, you should instead do:

delete obj.prop2;

The property prop2 will no longer will make an appearance when you're iterating through the properties.