Background

• Values, Types and Operators
• Program Structure
• Node.js REPL

Running JavaScript

In Code-OSS

• Activities -> Code - OSS
• Create a new file ~/fcshome/cs2613/labs/L08/hello-world.js
• Add some JavaScript code, save

    console.log("Hello world");

• Debug -> Start debugging (F5, same as DrRacket)

• Alternatively, select code with mouse, and "Run Code" from context menu. Note this is not a true REPL.

• Commit the file using the build in git support in code-oss

In a Browser

• Start Firefox

• Open the "Web Console" with Ctrl-Shift-K (or navigate via the "hamburger menu" to Developer tools).

• Select "Console"

• Copy-paste the code in.

Running a script

• open a terminal, find the right directory

  $ node hello-world.js

In the REPL

• Start up a node repl

  $ node

• Load your code into the repl

    > .load hello-world.js
  

• Evaluate some expressions

    > 1 + 1
    > "Hello " + "world!"
  

Translating Racket expressions into Javascript

• make a new file ~/fcshome/cs2613/labs/L08/expr.js and fill in the JavaScript expressions equivalent to the given Racket expressions.

  • You can test your solutions with the REPL either by pasting in the expressions, or by using .load.
  • Note that if you want to run your script from within code-oss, you will have to print the expressions with console.log

    //(string-append "Hello\n" "world!")

    //(* (+ 1 2 3) 7)

    //(< 41 (* 6 7))

    //(equal? (* (+ 1 2 3) 7) 42)

    //(equal? "Spongebob" "Squarepants")

    //(and (equal? (* 6 7) 42) (equal? "Spongebob" "Squarepants"))

    //(equal? 42 (if (< 3 5) (* 6 7) "turnip"))

    // (or #t (/ 1 0))

    // (and #f (/ 1 0))

Looping

• EJS2: Program Structure has documentation and examples for for and var.

• This section is based on Looping a Triangle; there are hints there if you get stuck.

• start a new file ~/fcshome/cs2613/labs/L08/loopy.js.

• Write a loop to generate the following text.

    #
    ##
    ###
    ####
    #####
    ######
    #######

• If you have extra time, step through your loop in the debugger.

Some weird JavaScript expressions.

• Follow along talk by Gary Bernhardt. Starting at about 1m25s, he talks about values in JavaScript. Which of Gary's examples is different (but still suprising) in the node repl?

• According to EJS 1, there are three "special numbers" in JavaScript: NaN, Infinity, and -Infinity. Find appropriate arithmetic expressions using integers that yield these three special numbers.

• In JavasScript, a variable that has been declared but not initialized is undefined. What is the equivalent in racket?

• You can also assign a variable to null. This is mostly like undefined, except it's an object reference. This interacts with JavaScript's Automatic Type Conversion in odd ways:

    > 8 * null
    > 8 * undefined
  

FizzBuzz (if)

Solve the famous FizzBuzz problem in JavaScript.

• This is essentially some nested ifs inside a for loop.

• If you have extra time, try to do both the obvious solution, and the tricky one hinted at in the text.