notes.md

Javascript Basics & Functions

Functions

• functions are defined with the keyword function
• Values are returned with the keyword return
  • There are no implicit returns in javascript.
• function defintions are expressions and objects, and are first class citizens
  • Functions can therefore be passed around like other pieces of data
  • Pass Functions as Arguments

Side Effects

• Things like console.log() are side effects because they don't return anything.
• Pure function:
  • One that has no side effects, nor depend or modify variables defined outside its current scope.
• Impure functions are functions that have 1 or more of those things.

Scope

• When in doubt define a varible with var. When you use var, you are declaring the var and assigning it
• Defining a variable globally with or without var doesn't make a huge difference.
  • Not declaring a variable with var makes it global by default.
• But when you define a variable inside a function, it makes a hunge difference.
  • var inside a function scopes the variable to the function only.
  • This means you can have multiple variable definitions with the same name in a different scope, as long as you declare with var
• When reassigning a variable that is already declared, you do not need var

Function Declaration vs. expressions

• Function declarations load before code gets executed.
• Function expressions load when the JavaScript reaches that line of code.
• You can call declared functions before they are defined, due to Hoisting.
• Hoisting does not effect function expressions. The functions are defined ad hoc (as the code is run)

Variable Hoisting