ECMA double fat arrow use?

Question

Can you explain this code? Is it currying?

    export const thing = (...items) => (wotsit) => {
        const thing = (props, {enums}) => {
            // ...
        };

        thing.contextTypes = {
            enums: PropTypes.object
        };

        return thing;
    };

    export default thing;

`=>` that lambda used for anonymous function, `export` are used to export function, variables which can be imported by other files — Shekhar Pankaj, May 10 '17 at 06:17

Danziger · Accepted Answer · 2017-05-10T06:25:33.990

4

Yes, it is. Without the arrow functions, it will look like this:

export const thing = function(...items) {

    // `items` will be an array with all the arguments that you pass in.

    return function(wotsit) {
        const thing = function(props, {enums}) {
            // ...
        };

        thing.contextTypes = {
            enums: PropTypes.object
        };

        return thing;
    };
};

export default thing;

On the other hand, this:

const thing = (props, {enums}) => {
    // ...
};

Is using parameters destructuring. It's the same as this:

const thing = (props, options) => {
    let enums = options.enums;
};

edited May 10 '17 at 06:25

answered May 10 '17 at 06:24

Danziger

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Shouldn't we use `bind` here, as you haven't used fat arrows in your code? – bharadhwaj May 10 '17 at 06:25
1

Just if you are using `this` inside any of those functions. See http://stackoverflow.com/questions/26477245/when-to-use-bind-in-js – Danziger May 10 '17 at 06:28
1

I guess it's the implicit return that threw me -- so much ECMA has all the legibility of early 1990's Perl code. The Perl community made implicit returns (and much else) socially unacceptable, I hope the ECMA peeps follow suit soon. Thanks for your help. – Lee Goddard May 10 '17 at 09:28

score 1 · Answer 2 · answered May 10 '17 at 06:17

It is returning back a function to be called at a later time. If the functions were not in ES6, it would look something like:

function thing(a, b) {
    return function(wotsit) {
        const thing = {};
        ...
        return thing;
    }
}

Which would eventually work something like this:

let a = thing(1, 2);
let b = a(wotsit); // Gives you back thing object

ECMA double fat arrow use?

2 Answers2