Commonly Asked JavaScript Puzzles

Commonly Asked JavaScript Puzzles

Recently, I have gone through various JavaScript interviews and I have composed a list which could help others as well.

These are just few and I would like to have more contributions from readers to enhance it more.

Please feel free to add more in comments.

Puzzle 1 (Closures)

/* 
   Write a mul function which behaves like below
   mul(1)(1)(1)(1)(1)(); return 5 
*/
function addNum(x) {
    return function(y) {
        if (typeof y !== 'undefined') {
            x = x + y;
            return arguments.callee;
        } else {
            return x;
        }
    }
}
console.log( addNum(1)(2)(3)() );

Puzzle 2 (delete operator on local variable)

// // What is the output 
var output = (function(x) {
    delete x;
    return x;
})(0);
console.log(output);
// output 0

Puzzle 3 (delete operator on Object)

// What is the Output 
var Employee = {
    company: 'xyz'
}
var emp1 = Object.create(Employee);
delete emp1.company
console.log(emp1.company);
// Output  'xyz'

Puzzle 4 (delete operator on Array)

// What is the output 
  var trees = ["xyz", "xxxx", "test", "ryan", "apple"];
  delete trees[3];
  console.log(trees.length);
// output 4

Puzzle 5 (Type conversion)

// What is the Output 
var bar = true;
console.log(bar + 0);
console.log(bar + "xyz");
console.log(bar + true);
console.log(bar + false);
// output 1 truexyz 1 2

Puzzle 6 (Variable Hoisting)

var salary = "9999";
(function() {
    console.log("Original salary was " + salary);
    var salary = "8888";
    console.log("My New Salary " + salary);
})();
// output undefined 8888

Puzzle 7 (Array Checking)

// How to check if an variable is array or not
function isArray(value) {
  return Object.prototype.toString.call(value) === '[object Array]';
}

Puzzle 8 (How to Empty an Array)

// // How to empty an array
var Uids = [1, 2, 3, 4];
newUids = Uids;
// Pattren 1 
Uids = [];
console.log(Uids);
console.log(newUids);
// Pattren 2
Uids.length = 0;
console.log(Uids);
console.log(newUids);

Puzzle 9 (What are closures and give an example of it)

function createFunction(x) {
    return function(y) {
        return x + y;
    }
}
var myFunc = createFunction(10);
console.log(myFunc(20));

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