Loop through arrays using Object.keys

I currently have two different iterations in my code:

For objects (snippet 1):

for (let key in object) {
    if (object.hasOwnProperty(key)) {
        // perform actions with key and object[key]
    }
}

For arrays (snippet 2):

for (let i = 0, length = array.length; i < length; i++) {
    // perform actions with i and array[i]
}

I want to simplify my code by using a single function for both objects and arrays (snippet 3):

let keys = Object.keys(objOrArray);
for (let i = 0, count = keys.length; i < count; i++) {
    // perform actions with keys[i] and objOrArray[keys[i]]
}

I am aware that snippet 3 works well for objects, but will it also work as expected for arrays, replacing both snippets 1 and 2? Will snippet 3 ensure key order (starting from index 0) in all browsers (at least those supporting Object.keys)?

[edit] I am planning to use this specifically for deep merging of objects. My current code is complex, with three branches at each level depending on the type (array, object, or other).

Answer №1

While the only enumerable properties on your array are the numbered slots (the default of an Array), there is no guarantee of the ordering of the returned properties as they are defined in for ( in ) order, which may not always iterate numerically depending on how the properties were assigned.

If you were to assign another property, it would also be enumerated, unlike with a more standard iteration technique.

The behavior is different for empty slots (e.g. new Array(25)) as the for loop would iterate over them.

It is generally recommended to use a for loop for an Array or the forEach() method (or similar methods).

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