Solution

one-liner-solution.js

/* 
 * If the loop bumps into an function, it returns true, and moves on,
 * but if it bumps into a number, it waits x milliseconds, 
 * it stops the _.every loop by returning false, and recursively 
 * calls the sequence function with the rest of the array.
 * Nifty, huh? 😝😝
*/
const sequence = b => b.every((a, i) => !(a.call ? a() : setTimeout(() => sequence(b.slice(++i)), a)));