Passing variables dynamically in a created Express.js route

Question

Passing variables dynamically in a created Express.js route

Creating routes in Express.js from a JSON file with the specified structure:

{
  "/home":{
    "token":"ksdjfglkas"
  },
  "/logout":{
    "token":"ksdjfglksaudhf"
  }
}

It is necessary to access the token within the routes function. The JavaScript code used for generating the route is as follows:

for(var endpoint in context){
  var route = context[endpoint];
  app.use(endpoint,
    function(req,res,next){
      req.token= route.token;
      next();
    },
    require('./route-mixin'));
}

The issue encountered is that the route-mixin method always receives the last token. In this case, 'context' refers to the JavaScript file mentioned above. How can different tokens be passed for each route individually.

javascript express

Answer 1

Answer №1

To solve this issue, I implemented a closure to encapsulate the content within the loop.

The problem was initially identified thanks to PhpStorm IDE: https://i.stack.imgur.com/4fQWz.png

Encountering the error message

mutable variable is accessible from closure

in the first middleware led me to seek guidance from this article Mutable variable is accessible from closure. How can I fix this?, suggesting the use of closures.

The simple resolution involved changing the code snippet from:

   for(var endpoint in context){
         var route = context[endpoint];
         app.use(endpoint,
             function (req, res, next) {
                 req.token = route.token;
                 next();
             },
             function (req, res) {
                 console.log(req.token);
                 res.send('test');
             }
         );
    }

to:

for(var endpoint in context){
    (function() {
        var route = context[endpoint];
        app.use(endpoint,
            function (req, res, next) {
                req.token = route.token;
                next();
            },
            function (req, res) {
                console.log(req.token);
                res.send('test');
            }
        );
    })();
}

The final example below demonstrates the functional solution that allowed the code to run successfully:

var express = require('express');
var app = express();

var context =  {
    "/home":{
        "token":"ksdjfglkas"
    },
    "/logout":{
        "token":"ksdjfglksaudhf"
    }
};
for(var endpoint in context){
    (function() {
        var route = context[endpoint];
        app.use(endpoint,
            function (req, res, next) {
                req.token = route.token;
                next();
            },
            function (req, res) {
                console.log(req.token);
                res.send('test');
            }
        );
    })();
}

app.listen(3000);

Answer 2

To solve this issue, I implemented a closure to encapsulate the content within the loop.

The problem was initially identified thanks to PhpStorm IDE: https://i.stack.imgur.com/4fQWz.png

Encountering the error message

mutable variable is accessible from closure

in the first middleware led me to seek guidance from this article Mutable variable is accessible from closure. How can I fix this?, suggesting the use of closures.

The simple resolution involved changing the code snippet from:

   for(var endpoint in context){
         var route = context[endpoint];
         app.use(endpoint,
             function (req, res, next) {
                 req.token = route.token;
                 next();
             },
             function (req, res) {
                 console.log(req.token);
                 res.send('test');
             }
         );
    }

to:

for(var endpoint in context){
    (function() {
        var route = context[endpoint];
        app.use(endpoint,
            function (req, res, next) {
                req.token = route.token;
                next();
            },
            function (req, res) {
                console.log(req.token);
                res.send('test');
            }
        );
    })();
}

The final example below demonstrates the functional solution that allowed the code to run successfully:

var express = require('express');
var app = express();

var context =  {
    "/home":{
        "token":"ksdjfglkas"
    },
    "/logout":{
        "token":"ksdjfglksaudhf"
    }
};
for(var endpoint in context){
    (function() {
        var route = context[endpoint];
        app.use(endpoint,
            function (req, res, next) {
                req.token = route.token;
                next();
            },
            function (req, res) {
                console.log(req.token);
                res.send('test');
            }
        );
    })();
}

app.listen(3000);

Passing variables dynamically in a created Express.js route

Answer №1

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