import - What does the require npm install module in node.js do?

Question

I just discovered that the require module will also affect subsequent require. Take moment and moment-timezone as an example, that is to say: /app.js {code...} But if I require moment-timezone first, I will require it later. moment, npm install moment, I still...

某草草 · Answer

1. Why after `require('moment-timezone')`, even if I don't `npm install moment` I can still `require('moment')` without getting an error?

View moment-timezoneDependencies

$> npm info moment-timezone dependencies 
{ moment: '>= 2.9.0' }

It can be seen that moment-timezone is dependent on moment, which means that moment will be automatically installed when installing moment-timezone, so it can be used without installing it separately.

2. Why does `require('moment-timezone')` affect the subsequent assignment of ｀moment` in `var moment = require('moment')`

View moment-timezonesource code

  1 //! moment-timezone.js
  2 //! version : 0.5.13
  3 //! Copyright (c) JS Foundation and other contributors
  4 //! license : MIT          
  5 //! github.com/moment/moment-timezone
  6 
  7 (function (root, factory) {
  8   "use strict";            
  9 
 10   /*global define*/        
 11   if (typeof define === 'function' && define.amd) {
 12     define(['moment'], factory);                 // AMD
 13   } else if (typeof module === 'object' && module.exports) {
 14     module.exports = factory(require('moment')); // Node
 15   } else {
 16     factory(root.moment);                        // Browser                  
 17   }
 18 }(this, function (moment) {
 19   "use strict";

On line 14, you can see that moment-timezone has modified require('moment'). As we all know, the npm module will be cached, so the subsequent var moment = require('moment') will be affected

By the way, directly modifying modules is the same as modifying global variables, which is not a good practice. The moment-timezone module here is basically a patch of the ｀moment｀ module and is a special case.

1. Why after require('moment-timezone'), even if I don't npm install moment I can still require('moment') without getting an error?

2. Why does require('moment-timezone') affect the subsequent assignment of ｀moment` in var moment = require('moment')

1. Why after `require('moment-timezone')`, even if I don't `npm install moment` I can still `require('moment')` without getting an error?

2. Why does `require('moment-timezone')` affect the subsequent assignment of ｀moment` in `var moment = require('moment')`