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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Removing Items From Arrays

why "length" is a property and not a method like pop or shift?

pop and shift are functions so is length, it does something and there is a code that counts and then returns the value, so why is it property?

2 Answers

Steven Parker
Steven Parker
228,077 Points

:point_right: In general, methods represent actions and properties represent data.

While you're no doubt correct that there is some computation going on behind the scenes, what's probably most significant about length is that it does not affect the state of the object it is applied to. On the other hand, both pop and shift make lasting changes to the object.

So, in keeping with that general principle, it makes sense that length would be implemented as a computed property and not a method.

Hi Art,

That's just the design choice that the JavaScript creators made. It makes sense, if you think about it. Functions are these mechanisms that take some optional input, perform some action(s) and optionally return some output. If you only really need the "perform some action(s)" and "return some output" part of this mechanism — if you don't need inputs — then it it would be reasonable to just make this mechanism a read-only property.

But, really, this type of thing is just how JavaScript was designed to be. Sometimes it's arbitrary, other times it's just following idioms that existed in previous languages, like C.