coding-questions.md

Coding Questions

Question: What is the value of foo?

var foo = 10 + '20';

Answer: '1020', because of type coercion from Number to String

Question: How would you make this work?

add(2, 5); // 7
add(2)(5); // 7

Answer: A general solution for any number of parameters

'use strict';

let sum = (arr) => arr.reduce((a, b) => a + b);
let addGenerator = (numArgs, prevArgs) => {
  return function () {
    let totalArgs = prevArgs.concat(Array.from(arguments));
    if (totalArgs.length === numArgs) {
      return sum(totalArgs);
    }
    return addGenerator(numArgs, totalArgs);
  };
};

let add = addGenerator(2, []);

add(2, 5); // 7
add(2)(5); // 7
add()(2, 5); // 7
add()(2)(5); // 7
add()()(2)(5); // 7

Question: What value is returned from the following statement?

"i'm a lasagna hog".split("").reverse().join("");

Answer: It's actually a reverse method for a string - 'goh angasal a m\'i'

Question: What is the value of window.foo?

( window.foo || ( window.foo = "bar" ) );

Answer: Always 'bar'

Question: What is the outcome of the two alerts below?

var foo = "Hello";
(function() {
  var bar = " World";
  alert(foo + bar);
})();
alert(foo + bar);

Answer:

• First: Hello World
• Second: Throws an exception, ReferenceError: bar is not defined

Question: What is the value of foo.length?

var foo = [];
foo.push(1);
foo.push(2);

Answer: .push is mutable - 2

Question: What is the value of foo.x?

var foo = {n: 1};
var bar = foo;
foo.x = foo = {n: 2};

Answer: undefined. Rather, bar.x is {n: 2}.

foo.x = foo = {n: 2} is the same as foo.x = (foo = {n: 2}). It is because a left term is first referenced and then a right term is evaluated when an assignment is performed in JavaScript. When foo.x is referenced, it refers to an original object, {n: 1}. So, when the result of the right term, {n: 2}, is evaluated, it will assigned to the original object, which is at the moment referenced by bar.

Question: What does the following code print?

console.log('one');
setTimeout(function() {
  console.log('two');
}, 0);
console.log('three');

Answer: one, three and two. It's because console.log('two'); will be invoked in the next event loop.