Rest and Spread operator examples

rest-spread.js

// Copying an array
let copy = [...arr]

// Creating an array of unique elements
let uniqueElements = [...new Set(arr)]; 
let elementsStartingWithA = [...new Set(arr)].filter(e => e.startsWith('a')); 

// Concatenate arrays
let concat = [...arr1, ...arr2]; 

// Slicing an array
let [firstElement, ...remainingArray] = arr;
let [, ...remainingArray] = arr; 

// Creating a copy of an object (this is not deep copy!)
let copy = {...obj}

// Merging objects
let merge = {...obj1, ...obj2}

// Conditionally adding properties to objects
let conditionalMerge = {...obj1, ...(condition ? obj2 : {})}}
let conditionalMerge = {...{ key1 : 1 }, ...(true ? { key2 : 2 }: {}), ...(false ? { key3 : 3 }: {})}

// Splitting a string to characters
let charactersArray= [...str]

// Destructuring and Rest Operator
let [a, ...b] = [1, 2, 3];
console.log(a); // 1
console.log(b); // [2, 3]