Declaring variable: [9 of 51]

• Three ways to declare variables in JavaScript:
  • var
  • let
  • const
  • For example:

      var one = 1;
      let two = 2;
      const three = 3;
    

• Each Keyword has its own purpose!
  • var
    • Original way to declare variables in JavaScript
    • A function scoped variable declaration, meaning that the variable, when defined, is available anywhere within that function.
    • The variable is even available in the function before it was declared.
    • The variable can be changed within the scope, meaning it is a immutable variable type. It can be reassigned, its data type can be changed
  • let
    • Similar to var
    • A block scoped variable declaration, meaning that the variable is only available within a block that has been denoted with a set of open and closed curly brackets
    • can be changed in scope
    • only usable after the declaration of the variable
  • const
    • Block scoped, like let
    • cannot be chaned
    • when you have set a variable that you have defined as a const, meaning a constant value, you cannot change what that assignment is
    • only available after declaration
• What to use when?
  • const by default
    • use as the “go-to” variable declaration
    • makes life easier for yourself and others when looking at your code, as it cannot be changed throughout the program and it will only have one value.
    • lower chance for bugs
  • let in loops
    • still very useful
    • use inside of a block scope when it is desirable to create a new variable every time the loop happens.
  • var
    • partially obselete, as let and const basically cover all of its use cases, and let and const remove some of the issues with using a var type variable declaration

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