advanced-spread-examples.js

let array1 = [1,2,3,4]

//Copying an array
let copyArray = [...array1]
copyArray.push(4)
console.log(array1)
console.log(copyArray)
/*
[ 1, 2, 3, 4 ]
[ 1, 2, 3, 4, 4 ]
*/

//**WARNING*/
let otherArray = [[1], [2], [3]]
copyArray = [...otherArray]
copyArray[0][0] = 3
console.log(otherArray)
console.log(copyArray)
/*
Spread does a shallow copy
[ [ 3 ], [ 2 ], [ 3 ] ]
[ [ 3 ], [ 2 ], [ 3 ] ]
*/

//Array concats
let array2 = ['a', 'b', 'c']

let result = [...array1, ...array2]
console.log(result)
//[ 1, 2, 3, 4, 'a', 'b', 'c' ]


//**WARNING */
let myString = "hello world"
let result2 = [...array1, ...myString] //totally valid but...
console.log(result2)
//[ 1, 2, 3, 4, 'h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd' ]

result2 = array1.concat(myString) //maybe this is what you really want
console.log(result2)
//[ 1, 2, 3, 4, 'hello world' ]

result2 = [...array1, ...array2, myString] //or this is valid too
console.log(result2)
//[ 1, 2, 3, 4, 'a', 'b', 'c', 'hello world' ]


//Merging objects
let myObj1 = {
    name: "Fernando Doglio",
    age: 34
}

let myObj2 = {
    name: "Fernando Doglio",
    age: 35,
    country: "Uruguay"
}

let mergedObj = {...myObj1, ...myObj2}
console.log(mergedObj)
// { name: 'Fernando Doglio', age: 35, country: 'Uruguay' }


//Cleaning up repeated elements from an array
let myArray3 = [1,2,3,4,4,4,4,2,3,3,4,6]
let mySet = new Set(myArray3)
myArray3 = [...mySet]
console.log(myArray3)
//[ 1, 2, 3, 4, 6 ]