Input and Output

• Computers can receive data from a keyboard, mouse, camera, microphone, etc.
  • These are called INPUTs
• Computers can also emit data like; text, graphics, sound, printing, etc.
  • These are called OUTPUTs

Memory vs I/O

• Performing calculations and using memory is fast
• Reading Input and writing Output is slow
  • CPU operations = nanoseconds, 1/1,000,000,000 second
  • I/O operations = milliseconds to seconds
• During an I/O operation, the program is paused, or waits.
  • CPU does other things during that time.

Using Readline

readline is a library, which is code you can use, but someone else wrote

Use Readline like the following example:

// include the library
const readline = require('readline');
// create an "interface", using STDIN and STDOUT
const readlineInterface = readline.createInterface(
  process.stdin, 
  process.stdout
);

// create a function called "ask" that
// OUTPUTs a question, and waits for INPUT
function ask(questionText) {
  // use a "Promise", which stands in for a future answer
  return new Promise((resolve, reject) => {
    readlineInterface.question(questionText, resolve);
  });
}

Echo Input with Readline

// make sure readline the code from the prior slide
// is included at the top of your file
async function echo() {
  console.log("Starting program...");
  let message = await ask("Say something, and I will echo!\n> ");
  console.log("You wrote:\n" + "=> " + message);
  console.log("Program complete...");
  process.exit();
}
// call the "echo" function
echo();

LAB: Echo

Create a new file called echo.js

• Include the readline library, readlineInterface, and ask function
• Add the code from the previous slide into the file
• Run echo.js using node, type an INPUT, and then press the [ENTER] key

Async and Await

A PROMISE is something that stands in for a finished result, while a task is still processing.

An example would be a ticket or receipt used to redeem an order from a food-truck.

Promises can be awaited, within a function marked as async.

1. await means "wait for the following to finish"
2. To use await inside a function, you must use mark it as async

WARNING: async functions and for loops do not mix well, use while instead

LAB: First and Last Name

Now it's your turn to write a program from scratch.

Write a program named name.js that asks two things:

1. Your first name
2. Your last name
3. Then it should output the following:

'Hello, {firstName} {lastName}!'

Replace the {firstName} and {lastName} with your INPUT values

First and Last Name solution

const readline = require('readline');
const readlineInterface = readline.createInterface(process.stdin, process.stdout);

function ask(questionText) {
  return new Promise((resolve, reject) => {
    readlineInterface.question(questionText, resolve);
  });
}

// include 'readline' and the 'ask' functions above
async function fullName() {
  let firstName = await ask("What is your first name? ")
  let lastName = await ask("What is your last name? ")

  console.log("Hello, " + firstName + " " + lastName + "!")
}

fullName()

LAB: What is your Quest

Create a file named quest.js.

Make the program ask three things:

1. "What is your name?"
2. "What is your quest?"
3. "What is your favorite color?"

After asking all three questions, the program should answer:

'Hello {name}! Good luck with {quest}, and here is a {color} flower for you.'

Solution: What is your Quest

// include 'readline' and the 'ask' function above
async function start() {
  let name = await ask('What is your name? ');
  let quest = await ask('What is your quest? ');
  let color = await ask('What is your favorite color? ');
  console.log('Hello ' + name + '! ' +
    'Good luck with ' + quest + ', ' +
    'and here is a ' + color + ' flower for you.');
  process.exit();
}

LAB: Name Length

Create a file name-length.js that:

• Calculates length of the first and last name INPUT combined
• Count only the non-blank characters.

Example:

What is your first name? Grace
What is your last name? Hopper
Hello, Grace Hopper!
Your name is 11 characters long.

NOTE: Whitespace, tabs, and new-lines are considered blank

LAB: Length of Each Name

Create a file allNamesLength.js that:

• Asks for a user's first name, middle name, and last name.
• Then prints the length of each individual name
• And finally prints the total character count for all three names.

Example:

What is your first name? Augusta
What is your middle name? Ada
What is your last name? King

Hello, Augusta Ada King!
Your first name is 7 characters long.
Your middle name is 3 characters long.
Your last name is 4 characters long.
Your full name is 14 characters long.