'use strict';

const cityPopulation = new Map();

cityPopulation.set('Shanghai', 24256800);
cityPopulation.set('Beijing',  21516000);
cityPopulation.set('Delhi',    16787941);
cityPopulation.set('Lagos',    16060303);

cityPopulation.delete('Shanghai');

if (cityPopulation.has('Beijing')) {
  console.log('Beijing:', cityPopulation.get('Beijing'));
}

if (!cityPopulation.has('Shanghai')) {
  console.log('no data for Shanghai');
}

console.log('size:', cityPopulation.size);
console.log('keys:', [...cityPopulation.keys()]);