How Can I Safely Iterate Over Object Properties in JavaScript Using `for...in`?

Iterating Object Properties with for...in

When iterating through object properties using the for...in loop, the loop variable propt represents the key of the property being accessed. However, it's not a built-in method or property for objects.

The for...in loop retrieves both properties from the object itself and properties inherited from its prototype. This can be problematic because inherited properties may not be intended to be included in the iteration.

Using hasOwnProperty for Accurate Iteration

To work around this issue, you can add a hasOwnProperty check within the for...in loop:

The hasOwnProperty method checks if a property is directly defined in the object, not inherited from its prototype. By using this check, you can exclude inherited properties from the iteration.

hasOwnProperty vs. Calling Through the Object

Alternatively, you can call hasOwnProperty through the object itself:

However, this may fail if the object has an unrelated field with the same name as hasOwnProperty, such as:

To avoid this issue, it's safer to call hasOwnProperty through Object.prototype instead:

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