In the simple words, when you execute the task asynchronously, the program moves to the next line of code before the task finishes. think of synchronous programming be like waiting in line, and asynchronous programming like taking ticket. When you take a ticket you can do other things and then be notified when ready. Promises are a far cleaner solution to writing asynchronous code.
A promise is a special object that contain their own condition.
- Pending - waiting
- Fullfilled - done
- Rejected - error
Промис(Обещание) — это объект который содержит будущее значение асинхронной операции. Например, если вы запрашиваете некоторые данные с сервера, промис обещает нам получить эти данные, которые мы сможем использовать в будущем.
Then method will check if the promise is resolve or rejected. For example if we have two promises: The waiter promises us to bring dish, and we in our side promises to pay to the dish if waiter brings it. In this situation then() method solves our case
Async and await makes the code more readable and understandable In short, this is asynchronous function that returns Promise.
Synchronous code is used when it is necessary to ensure that the code is executed in a strictly specified order. Asynchronous – in cases where the code may take a long time before finishing its execution, and at the same time its execution should not block the execution of other code.