WebFund 2013F Lecture 3

Audio from the lecture given on September 16, 2013 is available here.

Readings:

• Chapters 1-3, JavaScript: The Good Parts
• Chapters 1-2, Learning Node

Topics covered:

• REPL (read-eval-print loop)
• JavaScript quirks
  • Numbers are all floats
  • ambiguous comment characters
  • === equality
  • undeclared variables have global scope
• JavaScript objects and variables
  • loose typing
  • scoping
  • prototypes versus classes
  • JSON notation

notes

September 16

• history of JS
• REPL
• quirks
  • equality
  • numbers
  • comments
  • globals
• browser vs serverJS
• symbols and assignment
• object

history of JS

• nothing to do with java
• created over the course of a few weeks (~10 days) to script webpages
  • got into Netscape 2 in the late 90's
• not great, but got there at the right time, standardized
  • premature, rough draft, mistakes were made
• some amazing ideas, some so good that let you get around the rest of the issues
• don't think about C, don't think about Java, think about LISP
  • 2nd oldest language (goes back to late 1950's
  • modern variants - scheme (cleaner version)
  • LISP = LiSTProcessing
    • at the time, it was all about symbol programming

REPL

• Model
• Read
• Eval

basically evaluating all the time

• Print
  • output of print can almost always be sent to read
  • that means the data structure is in a format that can be read in
• Loop
• can do things incrementally, iteratively
• no compilation
  • no compile time errors, only ~runtime errors
• loosely typed - generally not statically typed
  • refers to the nature of the symbols you manipulate
  • in C x=5;
    • is storing the value of 5 somewhere in memory
    • int, double, short, char... etc
• in javascript x=5
  • • not ambiguous
    • y=x+5 won't give you an error until code is executed
• can write smaller programs that are more expressive
• some people hate javascript because of the browser
  • DOM - Document Object Model
    • ugly, painful, inconsistent
• quirks
  • write code to work on one browser, doesn't work properly on another
  • less pain than before, but still a factor
  • mobile stuff still being standardized

quirk #1

f = function(a,b) {
    x=7;
}

• wouldn't see this in something like C,
• in JavaScript it becomes a global variable
• have to specify that it is a local variable
• all symbols are seen globally by everyone else because there is no linker
• don't pollute global namespace

quirk #2

• comments can only be //, can't block comment

quirk #3

• equality operator is ===, for comparisons
• == does a shallow comparison

quirk #4

• no integer type
• can't do integer division without explicit truncates etc
• have to be conscious that you are using floats when doing numeric computations

var x = {
	color "red";
	model "unknown";
	};
	//this is an object, object notation

• property and value
• no classes

x.make = "?"
var x = {
	make"?";
	color "red";
	model "unknown";
	prototype : car;
	crash.function(velocity); // method
	};

• x.prototype is the same as car
• x.prototype.make="Tesla";
  • there is inheritance -- but it's weird
    • prototype-based inheritance
      • prototype : car;
    • x.model

• symbols can refer to any value, have no type
• browser vs server JS