Foundations of Javascript - Introduction

Values

• Primitive Values is data that is not an object and has no methods and properties. They are also immutable, you can replace the value but value can't be directly altered.
  • Numbers
  • Strings
  • Boolean
  • null
  • undefined
  • bigInt
  • symbol

      let varStr = "this is a string"
      varStr[0] = "T" //Replace 1st character
      console.log(varStr) //this is a string
      //Notice how the "T" doesn't replace the first character
      varStr = "Changed string"
      console.log(varStr) //Changed string
      //You can reassign new values, but can't modify the current value.
  

• Non-Primitive Values are objects. They are mutable, so you can directly modify the value without creating a new value.
  • array
  • functions

Operations

• Operands are objects that are being operated on
  • 3 + 4
    • 3 and 4 are operands
    • + is the operator
• Binary Operations have 2 operands involved
  • 3 + 4
• Unary Operations have 1 operand
  • ii++
    • ii is operand
    • ++ is operator

Types

• Values can have a specific data Types

•     typeof <value>
      //Tells you what type of data type the value is 
  

Variables

• A named reference to a value, you can access a value by calling its' name. These variables are stored in memory when they are created.

•   var varName = "String"
    var varNum = 100
  

Expressions vs Statements

• Expressions resolve to a value
• Statement is made up of multiple expressions and is the full sentence.

•   var varName = 100;
    //100 is an expression
    //varName is an expression
    //var varName is expression
    //varName = 100 expression
    //var varName = 100l; //is a statement
  

Condition Checking

• If Statement

    if(condition){
        //Do this if conditon is true
    } else {
        //If condition is false, then do stuff here
    }

Loops

• Repeats a operation depending on the context
• For Loops

    const arr = [1,2,3,4,5]

    for (let index = 0; index < arr.length; index++) {
        console.log(arr[index])
    }
    //Prints out array from elements 0 to 4

• For Each

    const arr = [1,2,3,4,5]
    //Goes through each element in array
    arr.forEach(element => {
        console.log(element)    
    });

• While Loops

    while(condition) {
        //do something until the condition is false.
        //Would need to do something here to change the condition to false otherwise it will loop forever
    }

Functions

• Collection of statements, that can be run by calling the function name

    function calcTotal(inputParams) {
        //Statement inside here
        //Do stuff with inputParams
    }
    calcTotal(1235); //Instead of copying the statements in the function, you can just call the function name. A shortcut
    
    //Functions can return a value so then you can assign a variable to the function call
    var total = calcTotal(123)