JavaScript implements blocking

Preface

JavaScript is a high-level scripting language that is widely used in web development and front-end development. In most cases, JavaScript is an asynchronous language that follows the pattern of event-driven programming, where functions are executed when an event is triggered. This makes JavaScript ideal for handling tasks related to UI user operations, such as DOM manipulation and AJAX requests.

However, sometimes we need to block the execution of JavaScript to ensure the synchronization and sequential execution of the code, especially in some complex scenarios, such as when we need to ensure that a certain function is executed before it is completed. Another function must wait for the result it returns. At this time, we need to use some techniques to implement JavaScript blocking.

This article will introduce some methods to implement JavaScript blocking, mainly including:

1. Use setTimeout
2. Use Promise
3. Use async/await
4. Use Generator

Use setTimeout to implement blocking in JavaScript

When we need to implement blocking in JavaScript, setTimeout is a very common method. setTimeout can create a timer to perform a specified task after a period of time. By setting the time parameter of the timer to 0, we can let the JavaScript executor execute the function in this timer after completing the current task. In this way, we can simulate JavaScript blocking.

The sample code is as follows:

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

async function demo() {
  console.log('Start');
  await sleep(5000); // sleep for 5 seconds
  console.log('End');
}

demo();

In this sample code, we define a function named sleep, which calls the setTimeout method and returns a Promise object. When we call the sleep method in the demo function, the JavaScript executor will wait for 5 seconds before executing subsequent code.

Use Promise to implement blocking in JavaScript

Promise is a very important asynchronous programming pattern in JavaScript. By using Promises, we can convert asynchronous operations into synchronous patterns, making it easier to keep code synchronized and readable.

The sample code is as follows:

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

function demo() {
  console.log('Start');
  sleep(5000).then(() => {
    console.log('End');
  });
}

demo();

In this sample code, we still use the sleep function to simulate the blocking operation, but this time we use the Promise object. When we call the sleep method in the demo function, it will return a Promise object. We can register a callback function by calling the then method, and execute this callback function when the Promise is completed. This time, instead of using the async and await keywords, Promise objects keep the code synchronized and readable.

Use async/await to implement JavaScript blocking

ES6 introduced the async/await keyword. Through these keywords, we can more easily handle Promise objects to implement JavaScript blocking operations.

The sample code is as follows:

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

async function demo() {
  console.log('Start');
  await sleep(5000);
  console.log('End');
}

demo();

In this sample code, we use the async and await keywords and place the sleep function inside an async function body. When we call the sleep method inside the demo function, it will automatically wait for the completion of the Promise object. This approach allows us to clarify the difference between blocking and non-blocking in the code and keep the code concise and readable.

Use Generator to implement JavaScript blocking

Generator is a special JavaScript function that can be interrupted and resumed. Generators can iterate over asynchronous tasks and be mixed with other control flows to implement blocking operations in JavaScript.

The sample code is as follows:

function* demo() {
  console.log('Start');
  yield sleep(5000);
  console.log('End');
}

function sleep(ms) {
  setTimeout(() => {
    it.next();
  }, ms);
}

const it = demo();
it.next();

In this sample code, we use the Generator function and put the sleep function inside it. When we call the yield keyword inside the demo function, it will pause the current execution state and wait for the execution of the sleep function to complete. When the sleep function is completed, the JavaScript executor will return to the demo function and continue executing subsequent code.

Conclusion

JavaScript is a very powerful and flexible programming language, and its asynchronous characteristics also make it a very excellent scripting language. But in some cases, we need to sacrifice some of its asynchronous features to achieve more sequential and synchronous operations. Through several methods introduced in this article, we can better control the execution process of JavaScript and write more robust and efficient code.

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