Map Object

ES6
Iterable like an array
It consists of key-value pairs like an object
However, unlike objects, maps can have any value as a key (Objects can only have strings or symbols as a key)

use methods to insert & delete values

  let jane = new Map();

  // insert with "set" method
  jane.set('id', 0);
  jane.set('name', 'jane');
  jane.set('major', 'international studies');
  jane.set('age', 27);

  // can also set with two dimentional array
  let amy = new Map([
      ['id', 1],
      ['name', 'Amy'],
      ['major', 'art'],
      ['age', 30]
  ]);

  //access Map with "get" method
  jane.get('age'); // 27

  // delete with "delete" method
  jane.delete('age'); // true (return boolean based on status)

  // clear all properties in Map with "clear" method
  jane.clear();

Why use?

Sometimes, using other data types than string or symbol as a key can be easier to understand

  const errorMsg = {
      404: "No such page",
      500: "Server error"
  }

  const errorMsg = new Map ([
      [404: "No such page"],
      [500: "Server error"]
  ])

  errorMsg.404 // unexpected number error
  errorMsg["404"] // "No such page"
  errorMsg.get(404) // "No such page"

using methods makes it easier to understand the intended action

can use for ...of loop

  let amy = new Map([
      ['id', 1],
      ['name', 'Amy'],
  ]);

  for (const [key, value] of amy) {
      console.log(key, value);
      // id 1
      // name Amy
  }