How to implement a function line in nodejs

NodeJs is a popular development platform. It is suitable for writing server-side applications outside of web browsers. It is characterized by an event-driven, asynchronous I/O and non-blocking IO model. The biggest advantage of NodeJs is its ability to handle concurrent requests. In this article, we will explore how to implement a function line using NodeJs.

What is a function line?

The function line is a linear execution path composed of multiple functions. When one function completes execution, it directs the next function to begin execution, and so on down the line. Function lines are often used for asynchronous processing, which can make the program simpler and clearer, and avoid the problem of callback hell.

How to implement function lines in NodeJs?

In NodeJs, we can use Promise to implement function lines. The Promise container is a container for the results of an asynchronous operation. It contains information about the final completion status of the asynchronous operation. The Promise object can have three states: pending, resolved and rejected.

• pending: Initial status, neither success nor failure status.
• resolved: means the operation completed successfully.
• rejected: means the operation failed.

We can use the Promise.then() method to connect multiple Promises to create a function line, which can handle asynchronous data very conveniently.

Below, we will demonstrate how to use Promise to implement a simple function line code.

function stepOne() {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      console.log("步骤一");
      resolve();
    }, 1000);
  });
}

function stepTwo() {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      console.log("步骤二");
      resolve();
    }, 1000);
  });
}

function stepThree() {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      console.log("步骤三");
      resolve();
    }, 1000);
  });
}

stepOne()
  .then(stepTwo)
  .then(stepThree)
  .catch(function(error) {
    console.log(error);
  });

In this example, we created three functions, namely stepOne, stepTwo and stepThree. Each function is an asynchronous operation and returns a Promise object. Among them, stepOne starts to execute, and then its resolve method executes, leading to the next function stepTwo to start executing, and then its resolve method leads to the final execution of stepThree. If an exception occurs in any step, we use the catch method to handle the exception.

Summary

This article briefly introduces how to use NodeJs to implement a function line. The advantage of using Promise objects to implement function lines is that the code is simpler and clearer, and can avoid the problem of callback hell. In NodeJs, we can connect multiple Promises through the Promise.then() method to create a function line.

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