Node向Angular返回响应时，res.send()外层加return的作用是什么？

Hey there! This is such a common gotcha when starting out with Express—let's break down exactly what's happening here.

First, let's clear up why both of your code snippets work when you test them:
In Express, methods like res.send() (or chained calls like res.status().send()) automatically end the HTTP response cycle. Once you call one of these methods, Express sends the data to the client and finishes processing the request. So even without adding a return, the response gets delivered successfully because the core action of sending the response is already completed.

So why bother adding that return? It's all about writing robust, bug-resistant code:

• Prevent unintended follow-up code from running：If your controller has conditional logic or additional code after the res.send() call, skipping the return can lead to hard-to-debug errors. For example:

  projectController.getProjectById = function(req,res){
    // Check if the required ID parameter is missing
    if (!req.params.id) {
      res.status(400).send("Project ID is required");
      // Without a return, the code below will still execute!
    }
    // This line will run even after we sent a 400 response
    res.status(200).send("Hey");
  }
  

  Running this would throw an error: Cannot set headers after they are sent to the client. That's because you're trying to send a second response after the first one already left the server. Adding return before res.send() in the conditional stops the function immediately, avoiding this mistake entirely.

• Make your code's intent clearer：Adding return acts as a clear signal to other developers (or future you) that this line is the end of the request handling for this branch of logic. It removes ambiguity about where the function stops executing, making your code easier to read and maintain.

Quick Summary #

• If your controller has no code after res.send(), both versions will behave identically.
• Using return res.send() is a best practice, especially in controllers with conditional logic. It prevents accidental duplicate responses and makes your code's purpose more explicit.

内容的提问来源于stack exchange，提问作者Pushprajsinh Chudasama