Implementing single execution of asynchronous functions in express

Question

Implementing single execution of asynchronous functions in express

Can anyone provide guidance on how to ensure asynchronous functions are only executed once within an Express application? I'd like to avoid running this function on every route and am seeking a more express-friendly approach.

var packageJson = false
app.use(function(req, res, next){
  if(req.packageJson) return next()
  if(packageJson){
    req.packageJson = packageJson
    return next()
  }
  return fs.readFileAsync("./package.json", "utf8")
  .then(JSON.parse)
  .then(function(data){
    packageJson = data
    req.packageJson = data
    return next()
  })  
})

javascript asynchronous express promise

Answer 1

Answer №1

I suggest refraining from running the asynchronous function within the initial call to that route. Instead, consider implementing the following code:

var jsonData = fs.readFileAsync("./data.json", "utf8").then(JSON.parse);
app.use(function(req, res, next){
  if (req.data)
    return next();
  else
    jsonData.then(function(data){
      req.data = data;
      return next();
    });
});

It is crucial to handle errors appropriately. If the promise for jsonData is rejected, your route may potentially hang indefinitely.

Answer 2

I suggest refraining from running the asynchronous function within the initial call to that route. Instead, consider implementing the following code:

var jsonData = fs.readFileAsync("./data.json", "utf8").then(JSON.parse);
app.use(function(req, res, next){
  if (req.data)
    return next();
  else
    jsonData.then(function(data){
      req.data = data;
      return next();
    });
});

It is crucial to handle errors appropriately. If the promise for jsonData is rejected, your route may potentially hang indefinitely.

Answer 3

Answer №2

For those looking for a specific solution (not a general one like @Bergi's), in this scenario you have the option of utilizing require(). This method provides two key advantages:

It is capable of directly loading JSON files
It stores file data in memory for efficient access

To implement this middleware, you can use the following code snippet:

app.use(function(req, res, next){
  req.packageJson = require('./package.json');
  return next();
});

Although the initial request may experience a slight performance hit due to the synchronous nature of require(), subsequent requests will benefit from automatic retrieval of data stored in memory.

Answer 4

For those looking for a specific solution (not a general one like @Bergi's), in this scenario you have the option of utilizing require(). This method provides two key advantages:

It is capable of directly loading JSON files
It stores file data in memory for efficient access

To implement this middleware, you can use the following code snippet:

app.use(function(req, res, next){
  req.packageJson = require('./package.json');
  return next();
});

Although the initial request may experience a slight performance hit due to the synchronous nature of require(), subsequent requests will benefit from automatic retrieval of data stored in memory.

Implementing single execution of asynchronous functions in express

Answer №1

Answer №2

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