The rest parameter (…args) vs the arguments object

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The rest parameter (…args) vs the arguments object

So I was listening to the Syntax.fm podcast, which is about various web development topics. In one of the episodes they were talking about the rest parameter, and one of the hosts had mentioned that they were using it often. I decided to check it out. According to Mozilla “the rest parameter syntax allows us to represent an indefinite number of arguments as an array.”[A] Just by looking at this statement, I realize how useful this could be. One scenario that crossed my mind was if we have an unknown number of arguments bein passed in, we can rely on the rest parameter to handle the acceptance, then use the functions logic to form a logic path based on the number of arguments being passed in.

Why not use the arguments array?

A good question would be, why care about the rest parameter, if JavaScript already has an arguments array? Well, the thing is, the arguments OBJECT is an ARRAY-LIKE STRUCTURE, meaning it’s not an array. It’s like an array, in that we can access arguments inside the “arguments object” by using indexed entries, such as argument[3]. Unlike an array, we cannot use array features such as map, push, pop, etc. As per Mozilla, it “does not have any Array properties except length.”[B] What the rest parameter does is place unnamed arguments inside an array, which we can manipulate as any other array.

Why use the arguments object at all?

The arguments object does still have it’s uses. Only unnamed parameters are placed in the rest parameter, so to access named parameters you still need to use their binding names, or reference their index in the arguments object. Another feature that the arguments object has is the callee function, which holds the current executing function. This itself can be it’s own topic, so I’ll let the reader look it up further for now.

In conclusion, both labels have their own reasons to be used, and I would like to think of them as complementary to each other.

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