JavaScript Puzzle: Questions With Interesting Answers

Questions

Question (1):

What is the value of typeof(NaN) ?

Question (2):

If 08 === 8 and 09 === 9 are true, then, will 010 === 10 be true?

Question (3):

Again.. If Infinity === Infinity and undefined === undefined, will both evaluate to true, Will NaN === NaN be also true?

Question (4):

In many programming languages division by zero will throw an exception, but in JavaScript, what will be the value of x when var x = 123 / 0; ?

Question (5):

You just learned that division by zero will evaluate to Infinity.. so you can tell what's the value of x when var x = 0 / 0; .. easy, right ?

Question (6):

If arr is an array, then arr.length will be increased or decreased after calling arr.push and arr.pop respectively. What is an easy way to make arr.length equals 50 ?

Question (7):

If null <= 0 is true, does that mean null < 0 or just means null == 0 ? (Hint: null >= 0 is also true)

Question (8):

If this code will show an alert message if ([]) { alert('hi'); }, what's the output of this if ([] == true) { alert('hi'); } ?

Question (9):

Which of the following will return true ?

• isNaN(true);
• isNaN(null);
• isNaN("");          // empty string
• isNaN("   ");         // string with one or more spaces

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Answers

Answer (1)

We all know that NaN is Not-A-Number, but some folks don't know that typeof(NaN) is "number".

Answer (2)

No, 010 is not equal to 10, because JavaScript will deal with any number that starts with "0" and contains no digits greater that 7, as an octal (base 8) number.

Answer (3)

No, NaN is not equal to NaN. (However, we don't blame JavaScript for that, it's the IEEE-754 spec for floating-point numbers).

Answer (4)

No, it will not be undefined, x will be Infinity.

Answer (5)

Exactly, x will be.. NaN.

Answer (6)

arr.length = 50; in Javascript you can set the length of the array to expand or trim it.

Answer (7)

Neither, both of them is false, although null <= 0 is true. It's all about how the '<=' operator coerces its operands.

Answer (8)

No alert, The '==' operator coerces the value of an empty array to 'false'.

Answer (9)

All of them will return 'false'

C# Puzzle: Questions on Extension Methods

Question (1):

What is the output of the following program ?

public class Program
{
    public static void Main()
    {
        var obj = new MyClass();
        obj.SayHello();
    }
}

public class MyClass
{
    public void SayHello()
    {
        System.Console.WriteLine("Hello, Original");
    }
}

public static class Ex
{
    public static void SayHello(this MyClass obj)
    {
        System.Console.WriteLine("Hello, Extension");
    }
}

Question (2):

What is the output of the following program ?

public class Program
{
    public static void Main()
    {
        var obj = new MyClass();
        obj.SayHello();
    }
}

public class MyClass
{
    
}

public static class Ex1
{
    public static void SayHello(this MyClass obj)
    {
        System.Console.WriteLine("Hello, Extension1");
    }
}

public static class Ex2
{
    public static void SayHello(this MyClass obj)
    {
        System.Console.WriteLine("Hello, Extension2");
    }
}

Answers

1. The program will print "Hello, Original", because when the instance method and the extension method both have the same signature, the instance method will always have higher priority.
2. The program will cause a compile-time error, because the call of "SayHello" function is ambiguous between two extension methods in classes "Ex1" and "Ex2".