循环内导入模块是一个坏习惯吗？

Question

I have a javascript module and I import it at the beginning of my main / main code and in it I execute a forEach, in this main code there is a loop that calls the methods of the module:

results.forEach(function(result) {
     for(const item of items .......){
        exampleModule.metodo(result, item)
     }
});

So far so good, the problem is that the values of the module are being mixed, the module is not dynamic according to the item Y of the result X, it kind of "disturbs" everything ...

I thought of a way to solve it, I do not know if it is the best practice, declare const exampleModule = require ('./modules/example.js') within an object and give that object a reference, such as item ID , since each ID will be unique:

let objetos = {}
results.forEach(function(result) {
     for(const item of items .......){
        objetos[item.id] = require('./modules/example.js')
        objetos[item.id].metodo(result, item)
     }
});

In short, I want each loop item to create an instance of the module without it being interfered with, if I instantiate the module in the item of position 0, everything in the module should only be used by that item 0, if it is item 1 the same thing, 1 n can change values of the module that is being used by position 0 and so on, is it possible? Can someone please help me?

Answer 1

I had the same idea, and checked it once, but it's basically a singleton what is returned by the require() function.

if you have

jQuery = require('jquery');
jQuery.fn.foobar = function() {
   this.css({color:red});
}

and then in another file you can do

$ = require('jquery');
$('hello').foobar();

The only condition is that the string you use to require() is the same case.

require('libs/myModule.js') != require('libs/mymodule.js');

behind the scenes a map is created:

 objects = {
    'jquery' : ....
    'add' : ....
    'strcasecomp' : ....
    '/www/htdocs/site/libs/myModule.js' : ...
 }

what happens when you require() is that if the object exists in the map, it's returned. If it doesn't exist, the relevant file is found, instantiated, mapped and returned.

Answer 2

Node.js caches the modules which are imported. So there's no side effect of requiring them in a loop. The caching is explained here in docs .

And yes, it's not best practice to import modules deep in the code as it's considered less readable. You can always do something like:

let objetos = {}
const exampleModule = require('./modules/example.js');
results.forEach(function(result) {
     for(const item of items .......){
        objetos[item.id] = Object.assign({}, exampleModule);
        objetos[item.id].metodo(result, item)
     }
});