JavaScript Maps

const rest = new Map(); // create new empty map  

// create map with values  
// This uses same structure (array of arrays) as Object.entries()  
const question = new Map([  
  ["question", "What is the best programming language in the world?"],  
  [1, "C"],  
  [2, "Java"],  
  [3, "JavaScript"],  
  ["correct", 3],  
  [true, "Correct 🎉"],  
  [false, "Try again!"],  
]);  

// set  
rest.set("name", "Classico Italiano"); // Add a key-value pair  
rest.set(1, "Firenze, Italy");  
console.log(rest.set(2, "Lisbon, Portugal")); // set also returns the map after adding item  
rest  
  .set("categories", ["Italian", "Pizzeria", "Vegetarian", "Organic"])  
  .set("open", 11)  
  .set("close", 23)  
  .set(true, "We are open :D")  
  .set(false, "We are closed :("); // Set calls can be chained too  

// get  
console.log(rest.get("name")); // get can be used to retrive value of a key  
console.log(rest.get("true")); // if key doesn't exist, undefinded is returned  

// using boolean keys  
const time = 8;  
console.log(rest.get(time > rest.get("open") && time < rest.get("close"))); // rest.get(8 > 11 && 8 < 23) -> We are closed :(  

// has  
console.log(rest.has("categories"));  

// size  
rest.size; // 7  

// delete  
rest.delete(2);  

// clear  
rest.clear();  

const arr = [1, 2];  
// rest.set([1, 2], 'Test');  
// rest.get([1, 2]); // This will return undefined, because the two arrays are different in the heap.  
rest.set(arr, "Test");  
console.log(rest);  
console.log(rest.size);  
console.log(rest.get(arr));  

rest.set(document.querySelector("h1"), "Heading");  

// Convert object to map  
const hoursMap = new Map(Object.entries(openingHours));  
console.log(hoursMap);  

// Convert map to array  
console.log([...question]); // Array of arrays of key-value pairs  
// = console.log(...question.entries());  
console.log([...question.keys()]);  
console.log([...question.values()]);