Java vs JavaScript: The 2020 Perspective

hello = (name = “Rebecca”)
console.log(“Hello, #{name}!”)
hello() # prints “Hello, Rebecca!”
hello(“Mary”) # prints “Hello, Mary!”

var client: string = ‘Mary’, // String
age: number = 26 // Numeric
function speak(name: string, age: number): void {
  console.log(name + “‘s age is “ + age);
}
speak(client, age);

export class Synchronizer {
  // … other code elided …
  synchronize = notConcurrent(async () => {
    let data = await this.gatherData();
    // more processing
    await this.sendDataToServer(data);
  });
}
// time A:
synchronizer.synchronize(); // => a promise
// a few seconds later, but before the sync has finished:
synchronizer.synchronize(); // => the same promise as before, no additional sync triggered

readFile("config.json")
  .then()
  .catch();
// This would be very difficult with callbacks
fetchJSON("/user-profile")
  .then(user => {
    return fetchJSON(`/users/${user.id}/relatives`);
  })
  .then(relativeIDs => {
    let promises = relativesIDs.map(id => {
      return fetchJSON(`users/${id};`);
    });
    return Promise.all(promises);
  })
  .then(relatives => console.log(friends));
fetchJSON("user-profile")
  .then(user => {})
  .then(relativesIDs => {})
  .then(relatives => {})
  .catch(error => {
    console.error("And error occurred.");
  });
function* generatorFunc() {
  let result = fetch("/users");
  // Pause execution by yielding
  yield result;
}
// Later something caused us to resume
console.log(`We're back!`);
function* generatorFunc() {
let result = fetch('/users');
// Pause execution by yielding
yield result;
  };
// Later something caused us to resume
console.log(`We're back!`);

class Foo {}
Typeof Foo // ‘function’

‘constructor.prototype’ to wire a parent code.

// name property is added at declaration
var obj = {
  name: "Mary"
};
//this would throw an error - sayYourName() is not declared yet
//obj.sayYourName();
// we add a new property at runtime
obj.sayYourName = function() {
  console.log("My name is " + this.name);
};
// and now it works
obj.sayYourName();