Once in a while, you may need to loop through Objects in JavaScript. The only way to do so before ES6 is with a for...in loop.
The problem with a ...
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While I generally agree with the message here (using
Object.keys()
,Object.values()
andObject.entries()
), I wouldn't generally recommend usingfor of
loop (or anyfor
loop for that matter). It doesn't work well with immutable data. Using pure functions likeArray.map()
,Array.forEach()
orArray.filter()
is generally better idea - you don't have to deal with side effects and it's generally easier to read.I totally agree with you regarding
for loop
and how.map
,.reduce
,.filter
are a heavenly match for functional programming. But there are cases where I feelfor of
loop is a natural fit:Iterator: Javascript now has native support for iterators (I talk about them in my article), so dealing with
Map
,Set
,Array
etc, thefor of
loop becomes a natural choice over converting these iterators to arrays and then applying the functional methods.Async: Another area I find
for of
loop a rather easier read is when I have to iterate through an async collection. I talk about some examples of async for loop here.I'd say this has more to do with your style, while I prefer these methods also, I've seen bunch of colleagues not understanding how these methods flow
it feels magical to them, they rather have a for-of (or a good old for) perhaps because my colleagues do tend to do more procedural stuff but y' know what works best for you is the way to go most of the time
but to reasure, I do prefer to use map, forEach, filter, and reduce when possible
Zell Liew, just wanted to add my 2cents to this well written article.
I feel if one realises that a particular
object
would require a lot of iteration then maybe they need to start thinking about ditching the object in favour of data structures which have a first party support for iteration.With ES6 we have a new fancy data structure called
Map
and it is a perfect fit for those cases where you are overloading an object with thousands of properties and also want to iterate through them.A simple example of
Map
.MDN Docs for Map
Thanks for adding on!
Under the "Looping through the array" section, in the first code example, you have:
This should be
key
, notkeys
:Nice and concise...very helpful thank you