Properly clearing properties

If you want to clear a property of an object, simply setting it to undefined won’t always cut it, based on how you will access/test the property later on:

// The setup
var obj = {
    prop: 1
};

// Clear property value
obj.prop = undefined;

The property is still attached to the object as a property and can be enumerated:

for (var key in obj) {
    // Will iterate through "prop"
}

typeof obj.prop == "undefined" // true
obj.hasOwnProperty("prop") // true -- it's still there!

To completely eliminate a property, you need to delete it:

delete obj.prop;

for (var key in obj) {
    // Won't iterate through "prop" anymore
}

typeof obj.prop == "undefined" // true
obj.hasOwnProperty("prop") // false -- it's gone completely!
Tags: beginner tips javascript