Solutions: Object Oriented JavaScript: 3. Functions

Previous: Chapter 2: Primitives

Chapter 3: Functions

1. Write a function that converts a hexadecimal color, for example blue "#0000FF", into its RGB representation "rgb(0,0,255)". Name your function getRGB() and this it with this code:

  var a = getRGB("#00FF00");
  a;       
  rgb(0,255,0)

  //Simple logic for getRgb()  

  var getRGB = function f(hexColor) {

    var result = "rgb(";   
    result += parseInt("0x"+hexColor[1]+hexColor[2]) + ", ";

    result += parseInt("0x"+hexColor[3]+hexColor[4]) + ", ";

    result += parseInt("0x"+hexColor[5]+hexColor[6]) + ")";

    return result;

  }    

  >> getRGB("#0000FF");

  "rgb(0, 0, 255)"

  >> getRGB("#00FF00");

  "rgb(0, 255, 0)"

2. What does each of these lines print in the console?

    >> parseInt(1e1)

    10    //1e1 is evaluated first

    >> parseInt('1e1')

    1  

    >> parseFloat('1e1')

    10    //parseFloat evaluates exponential in string

  

    >> isFinitie(0/10)

    true

    >> isFinite(20/0)

    false

    >> isNaN(parseInt(NaN));

    true

3. What does the following code alert()?

  >> var a = 1;

  function f() {

    var a = 2;

    function n() {

      alert(a);

    }

    n();

  }

  f();

    // It alerts 2. alert(a) has first access to the local variable a in f() which is defined as 2.

4. All these examples alert "Boo!". Can you explain why?

4.1  var f = alert; 

     eval('f("Boo!")');

f is assigned the function alert and eval executes the script in string by passing 'Boo!' as parameter.

4.2  var e;

     var f = alert;

     eval('e=f')('Boo!");

f is assigned the function alert and eval further assigns alert to e and executes the script in string by passing 'Boo!' as parameter.

4.3  (

       function() {

         return alert;

       }

     )() ('Boo!');

function() is a self invoking anonymous function that returns the method alert which is executed immediately by passing 'Boo!' as parameter.

Next: 4. Objects coming soon ...