1. Why do languages provide the switch statement, when we can achieve the same thing with multiple if... elseif statements? Show one example of how you might use the switch statement.
Switch statement is more readable and more versatile than multiple if...else if statements.
var Month = 13;
switch(Month)
{
case 1:
alert('January');
break;
case 2:
alert('February');
break;
case 3:
alert('March');
break;
case 4:
alert('April');
break;
case 5:
alert('May');
break;
case 6:
alert('June');
break;
case 7:
alert('July');
break;
case 8:
alert('August');
break;
case 9:
alert('September');
break;
case 10:
alert('October');
break;
case 11:
alert('November');
break;
case 12:
alert('December');
break;
default: alert('not a month of the year');
}
2. What is encapsulation, and what do functions encapsulate?
Wikipedia defines encapsulation in object-oriented programming as:
- A language mechanism for restricting access to some of the object's components.
- A language construct that facilitates the bundling of data with the methods (or other functions) operating on that data.
JavaScript functions encapsulate variables. The variables declared inside a function are not visible outside that function.
3. What is a pure function? Is the function show() provided in Eloquent Javascript a pure function?
Pure functions always return the same value when given the same arguments and never have side effects.
The function show() from Eloquent Javascript is not a pure function because it has the as side effect the text display on an output canal.
4. What do we mean when we say a variable in a function is shadowing a top level variable?
When we have a global variable and a variable declared inside of a function, both with the same name, the call of the variable will use the value set in that function.
var A=2;
function test()
{
var A=3;
print("A=" + A);
}
test();
// A=3 is printed
var A=2;
function test()
{
var A;
print("A=" + A);
}
test();
// A=undefined is printed
5. A recursive function, must have some sort of an end condition. Why would we get a "out of stack space" error message if a recursive function does not have an end condition?
Every time a function is called the context is stored on the stack. When function returns the context on top of the stack is taken off stack and resumed. A recursive function without an end condition will call itself endlessly running out of stack space very fast.
6. Reflect about the difference between object inheritance and class inheritance.
In object inheritance objects are derived from existing objects and then customized dynamically. All objects are ultimately derived from Object.prototype. It's much simpler than class inheritance that requires class definitions and object instantiations. Object inheritance provides simple inheritance vs. multiple inheritance provided in other languages with class inheritance.
7. What is object augmentation, and how do we do it?
By object augmentation new members can be added to any object at any time by simple assignment.
8. There is a way to add a method to String, such as any new String we create will have that augmented method (this is a bit different from object augmentation). How would you do this?
We have to augment String.prototype since all Strings derive from String.prototype.
9. What is garbage collection?
Garbage collection it's a mechanism based on mark-and-sweep principle. Javascript interpreter detects when an object will be never used again by the program and reclaims the memory, so the programmer doesn't have to keep track of memory allocation/deallocation.
10. What is the difference between an array and an object?
Arrays have a length member unlike objects.
Homework
1. Exercises 3.1 from chapter 3 of Eloquent Javascript
function absolute(num)
{
if (num >= 0)
return num;
else
return -num;
}
var num=-10;
print(absolute(num));
And cheeting...
function absolute(num)
{
return Math.abs(num);
}
var num = 11;
print(absolute(num));
2. Exercises 3.2 from chapter 3 of Eloquent Javascript
function greaterThan(num) {
return function(compared) {
return compared > num;
}};
var greaterThanNum = greaterThan(10);
show(greaterThanNum(15));
3.
3.1.
A dummy use of iterateAndOperate:
function fTest(a)
{
document.write(a);
}
var arr = new Array();
var s = '++++@++++';
arr = s.split('');
iterateAndOperate(arr, fTest);
fTest('<br>');
var s = '+++@@@+++';
arr = s.split('');
iterateAndOperate(arr, fTest);
fTest('<br>');
var s = '++@@@@@++';
arr = s.split('');
iterateAndOperate(arr, fTest);
fTest('<br>');
var s = '+++@@@+++';
arr = s.split('');
iterateAndOperate(arr, fTest);
fTest('<br>');
var s = '++++@++++';
arr = s.split('');
iterateAndOperate(arr, fTest);
A more inteligent use:
function pattern1(n)
{
var line = '';
for(i=0; i<(9-n)/2; i++){
line += '+';
}
for(i=0; i<n; i++){
line += '@';
}
for(i=0; i<(9-n)/2; i++){
line += '+';
}
document.write(line);
document.write('<br>');
}
var arr = [1,3,5,3,1];
iterateAndOperate(arr, pattern1);
3.2
function pattern2(n)
{
var line = '';
for(i=0; i<n; i++){
line += '*';
}
document.write(line);
document.write('<br>');
}
var arr = [1,3,5,3,1];
iterateAndOperate(arr, pattern2);
3.3
try
{
iterateAndOperate();
}
catch(error)
{
alert("Please provide parameters. " + error);
}
