You're not alone in this question; early on, lots of folks called `...` an operator. It isn't. Rest and spread are syntax, just like the commas in a function's parameter declaration list are syntax, not the comma operator. What rest and spread do is outside the realm of what an operator can do. An operator has a *single* result value which is (optionally) used where the operator's expression was once the expression has been evaluated. E.g., in `foo(2 * 5)`, the `2 * 5` is evaluated and the resulting value (`10`) is passed into `foo` as the first argument. Roughly speaking, operators are built-in functions with A) optionally-symbolic names, B) infix notation (for binary and ternary operators), and C) lazy argument evaluation; and like functions, they have only a single result value (and potential side-effects). Rest and spread can't be expressed that way. Consider `foo(...a)`. There's no single result value there, there's a series of discrete values used as discrete arguments to `foo`.
-- T.J. Crowder On Wed, Jul 5, 2017 at 1:40 PM, Andrew Li <[email protected]> wrote: > It seems as if there's two different ways to refer to the ... punctuator. > How should I refer to this: > > const foo = [bar, ...baz]; > > MDN seems to suggest it's referred to as 'spread syntax' but its article > URL seems to suggest it was initially created under the name 'spread > operator' -- and it's more popular when looking at Google results. Syntax > is the 'form' of the language while operators are generally used to perform > a certain operation on a number of operands to produce a value. > > It seems as if on the surface, 'operator' is the most appropriate fit > here, as it's seems more like a prefix unary operator more than it is > syntax. But in the context of ECMAScript, it's not listed as an operator at > MDN nor explicitly in the language specification -- and it's more of an > extension of array literal syntax and only works in context of array > literals. I would say it's more appropriately named syntax due to that, in > the language specification, it's only ever mentioned literally in the > ArgumentList and SpreadELement productions. That seems to suggest it's more > just syntax rather than a standalone operator such as + or *. > > Which way of referring to it would be more 'correct' if any and is my > reasoning correct? > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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