The parameters are essentially passed to function by value - so if the code within the body of a function assigns a completely new value to a parameter that was passed to the function, the change is not reflected globally or in the code which called that function.

function changeValueIntoC(value) {
	value = "C"
}

let myValue = "A"

console.log(myValue) // A
changeValueIntoC(myValue)
console.log(myValue) // A 

// The value won't change because the parameters are passed to function by value

When objects or arrays are passed, they are passed by reference.

function addNameToObj(obj) {
  obj.name = 'HI This is your name.'
}

const cat = {
  gender: 'boy',
  cute: true,
  age: 4
}

console.log(cat) // {gender: "boy", cute: true, age: 4}
addNameToObj(cat)
console.log(cat) // {gender: "boy", cute: true, age: 4, name: "MeowMeow"}

function pushValueIntoArray(arr) {
  arr.push('new value')
}

const myArray = [1, 2, 3, 4]

console.log(myArray) // [1, 2, 3, 4]
pushValueIntoArray(myArray)
console.log(myArray) // [1, 2, 3, 4, "new value"]

Javascript do hoisting

let a = 1

console.log(a)

function test1() {
  a = 3
  change(a)
  console.log(a)
}

function change() {
  console.log(a)
  a = 4
}

test1()

console.log(a)

// 1 - line 3
// 3 - line 13
// 4 - line 8
// 4 - line 20