Why is RequireJS not loading more than once a module I require multiple times?

Question

When there are two file import same module, it seems to share the same resource, like this:

main.js:

require(['cmdA', 'cmdB'], function(cmdA, cmdB){

})

cmdA.js:

define(function(require, exports){
    console.log('require: cmdA');
    var body = require('body');
});

cmdB.js:

define(function(require, exports){
    console.log('require: cmdB');
    var body = require('body');
});

result:

require body 
require: cmdA 
require: cmdB 

So why not :

require body
require: cmdA
require body
require: cmdB

I think body.js is required twice，so console outputs body twice. Why?

Answer 1

By default RequireJS treats modules as singletons. Once RequireJS does it's name resolution and finds that you want module X then if you require it once, twice, three million times, you'll always get the same module object. The first time the module is required, it is created, and then the next time it is required again, you get the same module as what was returned the first time. The callback you give to define is called once, and only once.

If you use requirejs.undef, you could trick RequireJS into giving you multiple copies of a module but this is not the basic usage.