ECMAScript 2015 Maps

Maps can be created iteratively by just calling set() as required:

const emails = new Map()
emails.set('Fred', 'fred@examle.com');
emails.set('Dave', 'dave@examle.com');

Alternatively you can pass the data in as an array of 2-item arrays during construction of the Map object.

const emails = new Map([
  ['Fred', 'fred@examle.com'],
  ['Dave', 'dave@examle.com'],
]);

Both approaches generate the same output.

Iterating over Maps

You can use a simple for-of loop to iterate over the keys and values.

const emails = new Map([
  ['Fred', 'fred@examle.com'],
  ['Dave', 'dave@examle.com'],
]);

for (let [key, value] of emails) {
  console.log(`The email address for ${key} is ${value}`);
}

// logs "The email address for Fred is fred@examle.com"
// logs "The email address for Dave is dave@examle.com"

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ECMAScript 2015 Maps

Iterating over Maps