Quiz: Javascript

Pitfalls

  1. What do the following expressions evaluate to?

    var k = "x";
var a = { x: 1, y: 3 };
a.x
a["x"]
a[k]
a.k

  2. What do the following expressions evaluate to?

    1 == true
1 === true
1 == "1"
1 === "1"

  3. What do the following expressions evaluate to?

    var x = 5;
function f(y) {
    var x = y * y;
    return y + x;
}
function g(y) {
    x = y * y;
    return y + x;
}
f(10);
console.log(x);
g(10);
console.log(x);

  4. What do the following expressions evaluate to?

    var x = 5;
function f() {
    var result = 0;
    for (var x=0; x<10; ++x) {
        result += x;
    },
    return result;
}
console.log(f());
var result = 0;
for (var x=0; x<10; ++x) {
    result += x;
}
console.log(result);

Objects

  1. What do the following expressions evaluate to?

    function create(x) {
    var result = {
        double: function() {
            this.value *= 2;
            return this.value;
        }
        value: x
    };
    return result;
}
   
var obj = create(1);
obj.double();
obj.double();
   
obj.triple = function() {
    this.value *= 3;
    return this.value;
}
obj.triple();

Functions, basics of functional programming

  1. What do the following expressions evaluate to?

    function f(x) {
    return x*x;
}
   
[1, 2, 3].map(f);
   
function odd(x) {
    return x % 2 === 1;
}
   
[1, 2, 3].map(f).filter(odd);

  2. What do the following expressions evaluate to?

    function makeFunction(x) {
    function f(k) {
        x += k;
        return x;
    }
    return f;
}
var a1 = makeFunction(3);
var a2 = makeFunction(3);
a1(1);
a1(3);
a1(5);
a2(1);
a2(3);
a2(5);