How to create asynchronous tasks in JavaScript

user_13635949 0
Viewed 382

How to do asynchronous tasks like this:

I want to have two tasks: One would print "foo" after 1 second, and the other one would print "bar" after 2 seconds. I want them to start at the same time, and run asynchronously.

Here's an example of this in python:

async def main():
    task1 = asyncio.create_task(
        say_after(1, 'hello'))

    task2 = asyncio.create_task(
        say_after(2, 'world'))

    print(f"started at {time.strftime('%X')}")

    # Wait until both tasks are completed (should take
    # around 2 seconds.)
    await task1
    await task2

    print(f"finished at {time.strftime('%X')}")

How do I do something like this in JavaScript? Do I use promises? I don't know how they work. I'm "new" to javascript

asynchronous-javascript task asynchronous javascript
4 Answers

You can use then method of js promises. 

function timeout(time_ms) {
  return new Promise(resolve => setTimeout(resolve, time_ms));
}


function main() {
  timeout(1000).then(() => console.log("hello"))
  timeout(2000).then(() => console.log("world"))

  var d = new Date();
  var n = d.toLocaleTimeString();
  console.log(`started at ${n}`)

}

main()

user_103031990

I strongly recommend you not to use async but Promise if you want to be good at JavaScript.

Promise is an expression that has a strong algebraic structure, and async-await, on the other hand, they are statements that has complicated rules.

user_170533590

Hi!

You can do it like this:

async function hello() {
  setTimeout(() => {}, 1000)
  console.log("hello")
}

async function world() {
  setTimeout(() => {}, 2000)
  console.log("world")
}

async function main() {
  await hello()
  await world()
}

main()

Let me know if that works for you!

user_159851200

Ok I figured it out:

async function foo() {
    return setTimeout(() => {
          console.log("foo")
        }, 1000);
}

async function bar() {
    return setTimeout(() => {
          console.log("bar")
        }, 1500);
}   

foo()
bar()
user_136359490
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