Background
Lerna is a tool that allows you to maintain multiple npm packages within one repository. There are multiple benefits of using such an approach - one repo, multiple packages. This paradigm is called monorepo (mono - single, repo - repository). You can read more about monorepo -
To summarise pros are -- Single lint, build, test and release process.
- Easy to coordinate changes across modules.
- A single place to report issues.
- Easier to set up a development environment.
- Tests across modules are run together which finds bugs that touch multiple modules easier.
Lerna Tutorial - Managing Monorepos with Lerna
First of all, you need to install lerna. Lerna is a CLI. To install it you need to execute following command -
- npm install --global lerna
- lerna -v
For me, it's 3.4.1 at the time of writing this post. Now let's create a directory for our lerna demo project. Let's call it lerna-demo. You can create it with the following command -
- mkdir lerna-demo
Now navigate inside this directory
- cd lerna-demo
- lerna init
It does following things -
- Creates packages folder. All packages go under this.
- Creates package.json at the root. This defines global dependencies. It has the dependency on lerna by default.
- Creates lerna.json at the root. This identifies lerna repo root.
- cd packages
Package - AdditionModule
Let's create a package that takes care of addition. Let's call it AdditionModule. Create a directory for this inside packages folder and execute following commands -
- mkdir AdditionModule
- cd AdditionModule
- npm init -y
module.exports.add = function(x,y){ return x + y; }
Save the file. This basically exposes add method to any other package that would have a dependency on this. Your 1st package is done. Let's create one more package for subtraction.
Package - SubtractionModule
Run similar commands inside packages folder -- mkdir SubtractionModule
- cd SubtractionModule
- npm init -y
module.exports.subtract = function(x,y){ return x - y; }
Save the file. This basically exposes subtract method to any other package that would have a dependency on this. Now let's create a package that would have a dependency on AdditionModule and SubtractionModule and can use add and subtract functions.
Package - Calc
Our final package - let's call it Calc would have a dependency on AdditionModule and SubtractionModule packages. So let's create the package 1st -
- mkdir Calc
- cd Calc
- npm init -y
Now create a file called index.js and add following content to it -
var add = require('AdditionModule'); var subtract = require('SubtractionModule'); var sum = add.add(2,3); var diff = subtract.subtract(3,2); console.log("Sum: " + sum + " Diff: " + diff);
Save the file. Now open package.json to add our dependencies. Edit package.json to add following content to it -
"dependencies": { "AdditionModule": "1.0.0", "SubtractionModule": "1.0.0" },
So your entire package.json looks like -
{ "name": "Calc", "version": "1.0.0", "description": "", "main": "index.js", "scripts": { "test": "echo \"Error: no test specified\" && exit 1" }, "keywords": [], "author": "", "license": "ISC", "dependencies": { "AdditionModule": "1.0.0", "SubtractionModule": "1.0.0" }, }
Now you are all set up. Your directory structure should look like below -
Now it's time to use lerna to link packages. Go to lerna-demo directory and execute the following command -
- lerna bootstrap
Now you can simply run calc index.js as follows -
- node packages/Calc/index.js
The important thing was the linking part that lerna does for you so that you do not have to worry about it.
For complete details on all available commands see - https://github.com/lerna/lerna
Related Links
- What is the purpose of Node.js module.exports and how do you use it?(OSFG)
- https://github.com/lerna/lerna
No comments:
Post a Comment