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
    }