Sunday, April 17, 2016

Creating a node module and using it

As you all knows, Node is getting better day by day and also there is an option of using node modules that are generated by other developers and are available to use.

Also, there is no good in making a Node project without user defined modules or in other words I can say that there is not possible (all though you can create a single module project but that is of no use) to generate the project in which you do not create the modules.

So, going forward Node modules are just the way of exposing a functionality from a Node file so that you can use that in other functions. For instance you want to create a calculator in Node js and for that you have decided that there would be four different modules namely add, subtract, division and multiply so that you can control them very gracefully and also tracing bugs would be easy since there are individual modules so when the bug got traced you can easily go to specific module in order to debug it.

So in order to do that, follow the steps:
  1. lets create a folder named node-calculator, for that browse to your docs and create a new folder either through right click and new folder or from shell using
    $ mkdir node-calculator 
  2. Go inside the folder using cd node-calculator and create one more directory named my_modules using :
    $ mkdir my_modules
  3. Now our basic setup is ready so we will code the things.
  4. Let us first create a module named add. 
  5. For that we will create a directory inside my_modules named add
  6. We will create a file inside add folder named index.js with following contents:
    var addition = function(a,b){
      return a+b;
    }
    
    module.exports = {
      addition_two_numbers  : addition 
    }
  7. In this the function addition is pretty simple and in order to expose that function to be useful in other files we have exported it with the name, addition_two_numbers
  8. Now create a file in node_calculator directory named calc.js with following contents:
    var add_module = require("./my_modules/add");
    console.log("Add module ", add_module.addition_two_numbers(2,2));
    
  9. Similarly create other modules named div, sub and mul. 
  10. Now the tree node-calculator command to see the contents and you will see something like this :
For your information:
  1. Code is available here
  2. The output shown at step 10 is of the command tree node_calculator
  3. If you don't have the tree command you can get it by:
    apt-get install tree
  4. In order to run the file use the node filename.js .
So for us it would be node calc.js and you will get the answer 4.

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