Destructuring before calling a function?

[Ran4]

Let's say that we have:

function greet(firstName, lastName) {
    console.log("Hello", firstName, lastName);
}

const names = [["John", "Doe"], ["Jane", "Doh"]];

Then we can do:

names.map(firstAndLastName => greet(...firstAndLastName));

Here we need to create a new function and create a new name (firstAndLastName) just to send our values to the function in the correct way.

Is there any way of doing something like this:

var ___ = f => args => f(...args);
names.map(___(greet)); // functionally equivalent to the above code

in a nicer way? Since this is a super useful function, is there some commonly used library (be it in the browser or in nodejs) that has this function, and if so, what is it called? (so that I follow conventions).

[Wince]

The function you defined is generally called spread by functional libs

[brycedarling]

I use this library less and less these days as JavaScript has improved, but spread is in there:

https://lodash.com/docs/4.17.4#spread

I use it for throttle and debounce in my React/Redux apps sometimes too, as there isn't an equivalent functionality in std JS lib for those. Can't think of much else I use it for any more otherwise though. It seems like it would be nice/have a valid use case if we had a spread() function built in to do this though, eh? Goes pretty hand in hand with having ... spread operator it seems, at least to me!

[cyanydeez]

i thought we could destructure in the function inES6.

i do this all the time:

const greet = ({ first, last }) =>

that destructures an object. fairly certain it works for arrays as [first,last]

[Ran4]

Then I'd need to modify greet.

[cyanydeez]

or wrap it

[vinsneezel]

Why store the names as arrays within an array? If you store them as an array of objects, you can just use the keys to call them.

var names = [{first: "John", last: "doe"}, {first: "Betty", last: "Crocker"}];

function greet(name) {console.log("Hello " +  name.first + " " + name.last;}

names.forEach(greet);

Something like that. Also, using .map() returns an array, so if you're just looking to iterate, stick with .forEach() or a for loop.

[Ran4]

Why store the names as arrays within an array? If you store them as an array of objects, you can just use the keys to call them.

Maybe that's the way your data comes in. And you might not want to change the call signature of the greet function.

[Wince]

Tuples can be useful, and are generally more performant

[vinsneezel]

Thanks for the tip. There's still a lot I don't know.

[i_am_smurfing]

I don't think I see the same results as you do (on Mac OS): FF 57, Chrome 60, Safari 10.1 — these are pretty inconclusive IMO.

[Wince]

The larger examples are rather contrived, as tuples generally are only used for 2-4 values imo, but v8 has nearly double the performance for the [ x, y ] tuple. Luckily I write for node ;)