Showing Revision 1 created 05/04/2012 by Amara Bot.

1. Title:
   03-38 Revenge Of Javascript
2. Description:

   dummy description

3. 0 0:00 - 0:05
   Now that we know how to specify grammars for well-balanced expressions
4. 5000 0:05 - 0:09
   and arithmetic and well-balanced webpage tags in HTML,
5. 9000 0:09 - 0:13
   we're going to return our attention to JavaScript.
6. 13000 0:13 - 0:17
   JavaScript is actually very similar to Python.
7. 17000 0:17 - 0:20
   Just like I showed you a formal grammar for HTML,
8. 20000 0:20 - 0:24
   we're going to work our way up to seeing a formal grammar for JavaScript.
9. 24000 0:24 - 0:27
   But before we get there, I just want to make sure
10. 27000 0:27 - 0:30
    that we really understand how JavaScript programs are interpreted.
11. 30000 0:30 - 0:35
    I'm going to show you a few more in Python and in JavaScript for comparison.
12. 35000 0:35 - 0:38
    Over here on the left, I have a Python function
13. 38000 0:38 - 0:41
    that computes the absolute value of its integer argument.
14. 41000 0:41 - 0:46
    If you give me a negative number, like -5, I will return positive 5.
15. 46000 0:46 - 0:51
    If you give me a positive number, like +9 million, I will return 9 million.
16. 51000 0:51 - 0:55
    The return value of this function is always either a zero a positive number.
17. 55000 0:55 - 0:59
    Now I'm going to write the same thing in JavaScript
18. 59000 0:59 - 1:01
    to provide for a comparison.
19. 61000 1:01 - 1:07
    Everything I've drawn in blue is a special keyword or punctuation mark used by the language.
20. 67000 1:07 - 1:11
    For example, to define a function in Python we use "def."
21. 71000 1:11 - 1:16
    In JavaScript, we write out the word function, but then it's still our choice what to call it--
22. 76000 1:16 - 1:18
    I'm called it "absval" in both cases--
23. 78000 1:18 - 1:21
    and how many parameters it should receive and what they're names are.
24. 81000 1:21 - 1:24
    In both cases, we have one parameter named x.
25. 84000 1:24 - 1:29
    In Python we use colons and tabbing to tell what the body of a function is,
26. 89000 1:29 - 1:33
    what the then branch for an if is, what the else branch for an if is.
27. 93000 1:33 - 1:38
    In JavaScript, we use curly braces and closing curly braces
28. 98000 1:38 - 1:42
    to denote this sort of lexical or syntactic scope.
29. 102000 1:42 - 1:46
    This is sort of curly brace 1, and it matches up with closed curly brace 1 over here,
30. 106000 1:46 - 1:50
    2 matches up with 2, and 3 matches up with 3.
31. 110000 1:50 - 1:55
    But in general the logical structure, the flow or the meaning, is the same.
32. 115000 1:55 - 1:59
    In both cases we check to see if x is less than 0, and we return 0 minus x in that case,
33. 119000 1:59 - 2:02
    or just x alone in the other case.
34. 122000 2:02 - 2:07
    One of the most important operations in any language is printing out information,
35. 127000 2:07 - 2:11
    displaying it to the screen so that we can see the result of computation
36. 131000 2:11 - 2:13
    or just to help us debug.
37. 133000 2:13 - 2:15
    In Python we use the print procedure.
38. 135000 2:15 - 2:17
    We pass it a bunch of strings.
39. 137000 2:17 - 2:20
    Here I'm adding together the strings "hello" and exclamation mart
40. 140000 2:20 - 2:23
    to make a very enthusiastic greet--"hello!"
41. 143000 2:23 - 2:26
    Over here on the right, I'm showing the same thing in JavaScript.
42. 146000 2:26 - 2:31
    The equivalent of "print" is "document.write" or perhaps just "write."
43. 151000 2:31 - 2:35
    In this class, we'll almost always abbreviate it down to just "write" to save space.
44. 155000 2:35 - 2:39
    If you're familiar with object-oriented programming, which is not required for this class,
45. 159000 2:39 - 2:41
    you might guess what the dot is about.
46. 161000 2:41 - 2:43
    We might talk more about that later.
47. 163000 2:43 - 2:48
    One of the key differences, though, is that all of our JavaScript functions have to have
48. 168000 2:48 - 2:51
    these open and close parentheses like a mathematical function
49. 171000 2:51 -
    has parentheses around its argument.