Difference between module exports and exports in the CommonJs Module System

Question

On this page  http   docs nodejitsu com articles getting-started what-is-require   it states that  quot If you want to set the exports object to a function or a new object  you have to use the module exports object  quot  My question is why     right module exports   function        console log  quot hello world quot        wrong exports   function        console log  quot hello world quot      I console logged the result  result require example js   and the first one is  Function  the second one is     Could you please explain the reason behind it  I read the post here  module exports vs exports in Node js   It is helpful  but does not explain the reason why it is designed in that way  Will there be a problem if the reference of exports be returned directly

User · Answer

node does something like this  module exports   exports       module exports and exports refer to same object  This is done just for convenience  so instead of writing something like this module exports PI   3 14  we can write exports PI   3 14  so it is ok to add a property to exports but assigning it to a different object is not ok exports add   function              this is OK and same as module exports add   function        exports   function              this is not ok and and empty object will be returned as module exports still refers to    and exports refer to different object

User · Answer

Also  one things that may help to understand   math js  this add   function  a  b        return a   b       client js  var math   require    math    console log math add 2 2      4    Great  in this case   console log this     module exports      true console log this     exports      true console log module exports     exports      true   Thus  by default   this  is actually equals to module exports   However  if you change your implementation to   math js  var add   function  a  b        return a   b      module exports         add  add      In this case  it will work fine  however   this  is not equal to module exports anymore  because a new object was created   console log this     module exports      false console log this     exports      true console log module exports     exports      false   And now  what will be returned by the require is what was defined inside the module exports  not this or exports  anymore   Another way to do it would be   math js  module exports add   function  a  b        return a   b       Or   math js  exports add   function  a  b        return a   b

User · Answer

Rene s answer about the relationship between exports and module exports is quite clear  it s all about javascript references  Just want to add that     We see this in many node modules     var app   exports   module exports          This will make sure that even if we changed module exports  we can still use exports by making those two variables point to the same object

User · Answer

module is a plain JavaScript object with an exports property  exports is a plain JavaScript variable that happens to be set to module exports  At the end of your file  node js will basically  return  module exports to the require function  A simplified way to view a JS file in Node could be this   var module     exports        var exports   module exports      your code  return module exports    If you set a property on exports  like exports a   9   that will set module exports a as well because objects are passed around as references in JavaScript  which means that if you set multiple variables to the same object  they are all the same object  so then exports and module exports are the same object  But if you set exports to something new  it will no longer be set to module exports  so exports and module exports are no longer the same object

User · Answer

As all answers posted above are well explained  I want to add something which I faced today  When you export something using exports then you have to use it with variable  Like  File1 js exports a   5   In another file File2 js const A   require  quot   File1 js quot    console log A a    and using module exports File1 js module exports a   5   In File2 js const A   require  quot   File1 js quot    console log A a    and default module exports File1 js module exports   5   in File2 js const A   require  quot   File2 js quot    console log A

User · Answer

myTest js  module exports get   function         exports put   function         console log module exports     output    get   Function   put   Function      exports and module exports are the same and a reference to the same object      You can add properties by both ways as per your convenience

User · Answer

Renee s answer is well explained  Addition to the answer with an example   Node does a lot of things to your file and one of the important is WRAPPING your file  Inside nodejs source code  module exports  is returned  Lets take a step back and understand the wrapper  Suppose you have   greet js  var greet   function         console log  Hello World        module exports   greet    the above code is wrapped as IIFE Immediately Invoked Function Expression  inside nodejs source code as follows    function  exports  require  module    filename    dirname      add by node        var greet   function               console log  Hello World                    module exports   greet      apply                                                       add by node  return module exports                                         add by node   and the above function is invoked   apply    and returned module exports  At this time module exports and exports pointing to the same reference    Now  imagine you re-write  greet js as    exports   function         console log  Hello World       console log exports   console log module exports     the output will be    Function       the reason is   module exports is an empty object  We did not set anything to module exports rather we set exports   function        in new greet js  So  module exports is empty    Technically exports and module exports should point to same reference thats correct     But we use     when assigning function       to exports  which creates another object in the memory  So  module exports and exports produce different results  When it comes to exports we can t override it    Now  imagine you re-write  this is called Mutation  greet js  referring to Renee answer  as   exports a   function         console log  Hello       console log exports   console log module exports     the output will be    a   Function      a   Function      As you can see module exports and exports are pointing to same reference which is a function  If you set a property on exports then it will be set on module exports because in JS  objects are pass by reference   Conclusion is always use module exports to avoid confusion   Hope this helps  Happy coding

[javascript] Difference between "module.exports" and "exports" in the CommonJs Module System

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