Coding Tutorials Blog

Javascript Basic Reference

February 07, 2021

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

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