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Faddah Wolf
12,811 Pointscan i use "For In" loops on JavaScript Arrays as well as objects?
Dave McFarland , et al.,
In the Objects section of your JavaScript Loops, Arrays & Objects modules, you introduce the "For In" loop to iterate through Objects. i believe this same method exists to loop through JavaScript Arrays, aslo, is that correct?
best,
ā faddah portland, oregon, u.s.a.
2 Answers
Stephen Gheysens
11,935 PointsHi Faddah Wolf! It certainly is possible, although if you care about ordering though (which is usually the argument for placing items into an array in the first place), you'll need to make a for loop that iterates through the indexes. From the MDN documentation: "Because the order of iteration is implementation-dependent, iterating over an array may not visit elements in a consistent order. Therefore it is better to use a for loop with a numeric index (or Array.prototype.forEach() or the for...of loop) when iterating over arrays where the order of access is important."
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in
Stephen Gheysens
11,935 PointsSo I'll admit can't actually find the source of the "difference in results" claim (I even just tried reading through the ECMAScript definitions of array iterators). I've read in many places (like here and here) that the it's bad practice because the elements aren't guaranteed to come out in order - I've always assumed they meant that the order the array elements are captured won't necessarily mirror the indexed order.
That aside, one prominent issue arises when the Array class has been extended with prototypal inheritance. For a clear explanation of Prototypal Inheritance, I'll leave it up to Andrew Chalkley https://teamtreehouse.com/library/objectoriented-javascript#prototypal-inheritance
Faddah Wolf
12,811 PointsFaddah Wolf
12,811 Pointsthanks! can you give an example, Stephen Gheysens , as to the differences in results? how can it not iterate over the array in order (i'm assuming, array indices 0, 1, 2, ...etc.)?
best,
ā faddah portland, oregon, u.s.a.