Javascript Basic Reference

Declaring Variables

const myVar = 1 can’t reassign, block scoped

let myVar = 2 can reassign, block scoped

var myVar = 3 can reassign, global unless in function

Math Operators

• +, - Add and Substract
• *, / multiply and divide
• ** exponent
• ++ increment (add one)
• -- decrement (subtract one)
• += add and reassign
• -= subtract and reassign
• *= multiply and reassign
• /= divide and reassign
• % modulo/modulus
• Math.random() generate random number (0-1)
• Math.ceil() round a number up
• Math.floor() round a number down
• Math.round() round a number
• Math.sqrt() square root of number
• Math.PI The numerical value of PI

Boolean Operators

• < > greater than, less than
• <= >= less equal, greater equal
• == === equality, strict equality
• != !== inequality, strict inequality
• && and
• || or

Conditionals

• IF statement

if (expression){
  //code if true
} else if (expression){
  //code if second expression is true
} else {
  //code if all expressions are false
}

• Ternary Operator

expression ? resultIfTrue : resultIfFalse

• Switch Statements

switch(value){
  case possibleMatch:
    //code if match
    break
  
  default:
    //code if no case matches
    break
}

Loops

• while loops

while(expression){
  //code to repeat as long as expression is true
}

• for loops

for(initiateCounter; expression; adjustCounter){
  //code will that will as long as expression is true
}

• for of loops

for (item of iterable){
  //code that will run for each item in iterable (array, set, map) and on each loop the current item will be stored in "item" 
}

• for in loops (for objects)

for(key in object){
 //loops over object keys, access value with object[key] 
}

• forEach Array Method

Array.forEach((item) => {
  // code to run for each item in the array, each item will take turns being stored in "item"
})

Functions

function myFunc(){
 //code to run when function invoked 
}

hoisted, can use this keyword

const myFunc = function(){
 //code to run when function is invoked 
}

not hoisted, can use this keyword

const myFunc = () => {
 //code to run when the function is invoked 
}

not hoisted, can’t use this keyword

Arrays

• const arr = [1,2,3] declare an array
• arr[0] access an array value
• const [one, two, three] = arr array destructuring
• const arrCopy = [...originalArr] copy array
• const dupeFree = [...new Set(arr)] remove duplicates

Objects

• const obj = {one: 1, two: 2} declare an object
• obj.one accessing property with dot notation
• obj["two"] accessing property with square brackets
• const {one, two} = obj object destructuring
• const objCopy = {...originalObj} copy an object

DOM Manipulation

• document.querySelector('h1') return the first matching node
• document.querySelectorAll('h1') return array of all matching nodes
• node.innerHTML property containing string to parsed as html in the node
• node.innerText property containing string to be parsed as text in the node
• node.style object containing all CSS properties of ndoe
• parentNode.appendChild(childNode) append a node as a child of a node
• node.addEventListener("click", someFunction) add event listener, function will run whenever specified event occurs
• document.createElement("h1") create a node