Compose takes in functions as arguments and returns a single function

compose.js

const compose = (...fns) => // 1. the spread operator torns function arguments into an array fns
 (arg) => // 2. a function is then returned that expects one argument arg
    fns.reduce( // 3. Reducing the fins with arg as the initial value
      (composed, f) => f(composed), // 4. Each function is called with the result of the previous functions
      arg  // 3.arg is the initial value
    )