delay.es

// wrapping into IIAFE to set strict mode,
// since otherwise chrome does not allow you to use let/const
(() => {
    "use strict"; 
    let delay = (fn, ms) => (...args) => new Promise(resolve => setTimeout(() => resolve(fn(...args)), ms));

    console.time("test");
    // Test:
    // we are delaying 5000 ms an arrow function that returns an array
    // with "Hello" concatenated with the given args, in this case "world"
    // and after executing this arrow function we are passing its result ([ "Hello", "world" ])
    // to another arrow function, which uses the comma operator to execute 2 expressions without
    // needing to wrap it with curly braces, where one of them logs the amount of time the test take to run,
    // and the other the arguments received, that are the ones fn returned when it was used to set
    // the promise resolution value, therefore [ "Hello", "World" ], and we are using the spread operator
    // so it will end up printing "Hello World" after 5000 ms
    // (3 lines of code, 9 lines of comments :P)
    delay((...args) => [ "Hello", ...args ], 5000)("World")
        .then(args => (console.timeEnd("test"), console.log(...args)));
})();