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javascriptfeathersjs

Arrow function ES6

I have a basic understanding of arrow functions. I however came across this piece of code and am some what stumbled.

const errors = require('@feathersjs/errors');

const test = () => async context => {
   //omited
}


module.exports = {
  before: {
    all: [],
    find: [],
    get: [],
    create: [test()],
    update: [],
    patch: [],
    remove: []
  },  
 };

What exactly is this line doing ?

const test = () => async context =>

It looks like some form of double arrow functions?

I am including the hooks code as it is part of the library feathersjs and this function is writing a hook before a particular call.

Solution

  • If you are not passing curly braces, then the arrow function by default returns the value you're pointing it to. So think of it this way,

    let testValue = () => 'some value';

    is the same as

    let testValue = () => {
   return 'some value';
};

    So your function can be written as

    let test = () => {
   return async context => {
       // some process
   }
};

    Basically the function is returning another function, this is called Currying and is a way of creating higher order functions and helps avoid repeatedly passing some values. For example, if I have a helper function which helps me create a multiplier

    let multiplier = (x) => (y) => x * y;
let multiplyBy5 = multiplier(5);

console.log(multiplyBy5(5)); // 25

    I basically created a function multiplyBy5 which creates a function to multiply my values by 5, and I can create more multipliers for different values.