CODEWITHSUNDEEP
node.jsglobal-variablesrequire
Alex Seville
Alex Seville

Reputation: 178

Global variable vs. require.cache in NodeJS

I know using the global variable is discouraged in node, but assuming I need to store some data globally, which is a worse approach:

  1. using global

  2. Using the require cache directly to store an object, i.e.

    require.cache["myGlobalVar"] == {};

I suspect that option 2 is worse because the require cache is intended to be used for modules.

More details: I thought about using require("myLibrary").myGlobalVar but that would require having myLibrary accessible to all the files calling it, which might not be possible in practice. I'm making a code coverage tool so I can expect the user to install "myLibrary" in their dev/test modules, but not necessarily in their src node_modules directory, to which the instrumented code files would refer.

Upvotes: 6

Views: 13804

Answers (3)

Harsh Srivastava
Harsh Srivastava

Reputation: 390

Every time, when you require cache file, it will trigger the function again and initialize the cache object again.

var cache = {}

to solve this we can implement the cache like mentioned below: 

//cache.js
module.exports = {
    cache: {},
    get: function (key) { return this.cache[key]; },
    set: function (key, val) { this.cache[key] = val; },
    dumpCache: function () { return this.cache } // this just for testing purpose
}

// index.js

var cache = require('./cache');

cache.set('12', 'Hey');
console.log(cache.get('12'));
console.log(cache.dumpCache());

Upvotes: 1

jox
jox

Reputation: 2368

The answer from Bill didn't work for me because it can in fact not be used "from any place by require'ing it". This is because it's exporting a function that is called on each require and thus creating a blank new (empty) cache each time.

The solution is exporting an instance of the function...

// cache/memoryCache.js
module.exports = function () {
    var cache = {};
    return {
        get: function (key) { return cache[key]; },
        set: function (key, val) { cache[key] = val; }
    }
}();

...and then requiring that very instance each time.

// some other file
var cache = require('../cache/memoryCache');
cache.set('1234', 'value I want to share');
cache.get('1234');  // 'value I want to share'

(Note the difference: the pair of parenthesis "()" is now at the end of the function definition in the module and not after the require.)

Upvotes: 13

Bill
Bill

Reputation: 25555

Why don't you just create an in memory cache that all of your other code can then reference?

var memoryCache = module.exports = function () {
    var cache = {};
    return {
        get: function (key) { return cache[key]; },
        set: function (key, val) { cache[key] = val; }
    }
}

You can then use the cache from any place by require'ing it.

var cache = require('../cache/memoryCache')();
cache.set('1234', 'value I want to share');
cache.get('1234');  // 'value I want to share'

Upvotes: 14

Related Questions