How Does JavaScript's `for...in` Loop Actually Iterate Through Object Properties?

Iterating Through Object Properties

In JavaScript, the for...in loop can iterate through the properties of an object. However, it's important to understand how the loop variable propt represents these properties.

Initially, it might seem puzzling that propt is not a built-in method or property of objects. Instead, it is a variable that is assigned each property name during the loop iteration.

The loop iterates over the object's keys, which are always strings. This includes inherited properties from the object's prototype chain, as well as custom properties defined on the object itself.

To avoid issues with inherited properties, it's recommended to use the hasOwnProperty method to distinguish between custom properties and inherited properties:

for (var prop in obj) {
    if (Object.prototype.hasOwnProperty.call(obj, prop)) {
        // Do stuff with custom property prop
    }
}

This ensures that only custom properties are iterated over. Additionally, you can call hasOwnProperty directly through the object itself, but it's safer to use the Object.prototype version to avoid potential conflicts with custom properties with the same name.

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