Some brain-burning Javascript questions
November 11 2016

Some of the questions are tricky, the others are traps. All of them are fun.

Print numbers 1 - 10 with 1 second lag - Beepi

// use setTimeout
function print(n) {
    console.log(n);
    if (n < 10) {
        setTimeout(() => {
            print(++n);
        }, 1000);
    }
}

print(1);
// use setInterval
function print() {
    var n = 1;
    console.log(n);
    var interval = setInterval(() => {
        n++;
        console.log(n);
        if (n === 10) {
            clearInterval(interval);
        }
    }, 1000);
}

print();
// for loop & IIFE
for (var i = 1; i <= 10; i++) {
    setTimeout(() => {
        console.log(i);
    }, i * 1000);
}

If sum(1, 2, 3) === 6, make the following also work: sum(1)(2, 3), sum(1, 2)(3), sum(1)(2)(3) - Beepi

function sum() {
    // convert arguments to array
    var args = Array.prototype.slice.call(arguments);

    function getTotal() {
        return args.reduce((a, b) => a + b);
    }

    if (args.length !== 3) {
        return function(a) {
            for (var i = 0; i < arguments.length; i++) {
                args.push(arguments[i]);
            }
            return sum.apply(null, args);
        }
    } else {
        return getTotal();
    }
}

console.log(sum(1)(2)(4)); // -> 7
console.log(sum(1, 2)(4)); // -> 7
console.log(sum(1)(2, 4)); // -> 7

Create a cache function to cache functions that took 2s to run

For example, complexFunction has a runtime of 2s. The cachedFunction has a runtime of 2s when it first runs, and later it will return the result instantly. All functions that need to be cached will return a value and has no other side effects

var complexFunction = function(arg1, arg2) {
    return arg1 + arg2;
};

// complexFunction(1, 2); -> 2s
// complexFunction(1, 2); -> 2s

var cache = function(func) {
    var map = {};
    return function() {
        var key = '';
        for (var i = 0; i < arguments.length; i++) {
            let key = JSON.stringify(Array.prototype.slice.apply(arguments));
        }
        if (!map.hasOwnProperty(key)) {
            map[key] = func.apply(null, arguments);
        }
        return map[key];
    }
};

var cachedFunction = cache(complexFunction);

// cachedFunction(1, 2); -> 2s
// cachedFunction(1, 2); -> 0s

Create the all() function that achieve this [1, 2, 3].all(isGreaterThanZero); -> true

var isGreaterThanZero = function(num) {
    return num > 0;
};

Array.prototype.all = function(func) {
    for (var i = 0; i < this.length; i++) {
        if (!func(this[i])) {
            return false;
        }
    }
    return true;
};


[1, 2, 3].all(isGreaterThanZero); // true
[-1, 2, 3].all(isGreaterThanZero); // false

Reverse an array without using loop - SigFig

// use recursion
var a = [1,2,3,4,5];

function swap(array, i, j) {
    var temp = array[i];
    array[i] = array[j];
    array[j] = temp;
}

function reverse(array, i) {
    if (i < Math.floor((array.length - 1) / 2)) {
        swap(array, i, array.length - 1 - i);
        reverse(array, i + 1);
    } else {
        return;
    }
}

reverse(a, 0);
console.log(a);

Write a debounce function

(function() {
    function debounce(func, wait) {
        var timeout = null;
        return function() {
            var that = this;
            var arg = arguments;
            if (timeout == null) {
                func.apply(this, arg);
                timeout = setTimeout(function() {
                    clearTimeout(timeout);
                    timeout = null;
                }, wait);
            }
        }
    }

    var efficent = debounce(function(e) {
        console.log(e.type);
    }, 1000);

    window.addEventListener('resize', efficent);
})();

Decompress 3[abc]2[d]ef -> abcabcabcddef - Google

Calculate (add (mul 2 3) 3 1) - Affirm

CURRENTLY

Software Engineer at Yahoo!

PREVIOUSLY

Full Stack Engineer at Prosper Marketplace

PREVIOUSLY

Front End Engineer at BillGuard (Acquired by Prosper)