aChainAddingFunction.js

/**
 * Description:
 *
 * We want to create a function that will add numbers together
 * when called in succession.
 *
 * add(1)(2);
 * // returns 3
 * We also want to be able to continue to add numbers to our chain.
 *
 * add(1)(2)(3); // 6
 * add(1)(2)(3)(4); // 10
 * add(1)(2)(3)(4)(5); // 15
 * and so on.
 *
 * A single call should return the number passed in.
 *
 * add(1) // 1
 * We should be able to store the returned values and reuse them.
 *
 * var addTwo = add(2);
 * addTwo // 2
 * addTwo + 5 // 7
 * addTwo(3) // 5
 * addTwo(3)(5) // 10
 * We can assume any number being passed in will be valid javascript number.
 */
function add(n) {
    let sum = n;
    const proxy = new Proxy(()=>{}, {
        get () { return () => sum},
        apply (...args) {
            sum += args[2][0]
            return proxy
        }
    })
    return proxy
}