RTFM

• docs.nodejs.org
• devdocs.io
• stackoverflow.com

On devdocs.io, enable:

1. JavaScript
2. Node.js (your version!)
   
   

Node or Javascript?

1. console
2. Promise
3. url.parse method
4. alert function

GIYF

Google Is Your Friend

TIAS

Try It And See

Datatypes

Objects

var me = {
  first : 'Sequoia',
  last  : 'McDowell',
  age   : 31
};

console.log(me.age); // 31

var me = new Person('Sequoia', 31);

console.log(me.age); // 31

var me = ['Sequoia', 'McDowell', 31];

console.log(me[2]); // 31

Datatypes

Primitives

• Boolean
• Null
• Undefined
• Number
• String
• Symbol (new in ES6)

Type system

"Dynamic" "Duck"

typeof

instanceof

Function Declaration

function add(x, y){
  return y + x;
}

add(1,2);  // => 3
function add(x, y){ return y + x; }
add(3,2);  // => 5

Create divide & multiply functions:

// javascript-review/start/mul-and-div.js
console.log(
  div(
    mul( 21, 40 ),
    mul(10, 2)
  )
);

//output: 42

//same thing on one line:
console.log( div( mul(21, 40), mul(10, 2) ) );

• Run with node filename.js

Function Expressions

What's meant by "expression"?

"any valid unit of code that resolves to a value." - MDN

Expressions

(1 + 1)                           //expression
("hello world")                   //expression
(function(){ return 21; })        //expression

(1 + 1)                           //=> 2
("hello world")                   //=> "hello world"
(function(){ return 21; })        //=> function(){ return 21 }

typeof (1 + 1)                    //=> "number"
typeof ("hello world")            //=> "string"
typeof (function(){ return 21; }) //=> "function"

var sum = 1 + 1;
var msg = "hello world";
var fun = function(){ return 21; };

Function Expression

var add = function(x, y){
  return y + x;
};

add(1,2);  // Uncaught TypeError: add is not a function
var add = function(x, y){ return y + x; };
add(3,2);  // => 5

Function Expression

anonymous

var add = function (x, y){
  return y + x;
};

named

var add = function add(x, y){
  return y + x;
};

Function Expressions

Why use named expressions?

Uncaught TypeError: Cannot read property 'name' of undefined
  getUser              @ foo.js:2
  (anonymous function) @ bar.js:71
  (anonymous function) @ bar.js:202
  (anonymous function) @ baz.js:11
  ...

Uncaught Error:
  getUser              @ foo.js:2
  getItem              @ bar.js:71
  buildDBQuery         @ bar.js:202
  createDatabase       @ baz.js:11
  ...

Find where I broke the "Always use named expressions" rule and rewrite it as a named expression

javascript-review/start/function-runner.js Create a function that takes a function argument and...

1. outputs the name
2. executes the function

Hints:

1. myfunction.name

Extra Credit:

1. run returns a function that does 1 & 2 above

    var wrappedHello = run(helloworld)
    wrappedHello();
   

Up Next: Handling Functions

Example: setTimeout

//filename: javascript-review/set_timeout_example.js

//setTimeout( FUNCTION , NUMBER );

var sayHi = function logHello(){
  console.log('hello');
};

var delay = 500; //ms

setTimeout(sayHi, delay);

Up Next: Scope & Hoisting

Variables & functions stay in the scope in which they are declared

Declarations

• Variable Declarations

   var x;
   var y;
  

• Function Declarations

   function three(){
     return 3;
   }
  

Which x?

var x = 99;       // declared in outer scope

function addTen(y){
  var x = 10;

  return y + x;
}

console.log(addTen(7)); // ??
console.log(x);         // ??

A scope has access to its parent scopes

var x = 99;       // declared in outer scope

function addTen(y){
  x = 10;

  return y + x;
}

console.log(addTen(7)); // ??
console.log(x);         // ??

Always use var to declare vars when creating them!!

function myDictionary(){
  $ = 'dollars';
  _ = 'no dollars';
  angular = 'the opposite of round';
}

congrats-server.js:

Create a server that...

1. says "CONGRATULATIONS!" to the 5th visitor

Hints:

1. functions can access variables outside their own scope
2. boilerplate in javascript-review/start/

Assignments are not hoisted

console.log(x);

var x = 100;

Interpreter sees:

var x;

console.log(x);

x = 100;

What will this do?

var x = 123;

console.log(x);
console.log(y);
console.log(z);

var y = 456;
z = 789;

1. 123
2. undefined
3. (throws error)

Review

add(1,2);  // => 3
function add(x, y){ return y + x; }
add(3,2);  // => 5

add(1,2);  // Uncaught TypeError: add is not a function
var add = function(x, y){ return y + x; };
add(3,2);  // => 5

Up Next: Asynchronous Programming