In this article, we are going to make React component that will be available as an NPM module. So we can use this component in different projects. You will find this article useful if you are going to build a custom time picker. Let’s dive in! Code from this example you can find in this repo.

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time-picker by


Create-react-app is a great tool for bootstrapping the front-end project, and I always use it for new projects. However, since we want to make an NPM module, we need a different starter. After some research, I found a tool, named create-react-library that using create-react-app to run demo and rollup to build our library. To start a new project, we will type these commands:

$ npm install -g create-react-library
$ create-react-library increaser-timepicker
$ cd increaser-timepicker

After initializing our project, we will install the only additional library we will need.

$ npm install --save styled-components

And add additional fields in the rollup.config.js file.

external: ['styled-components'],
globals: { 'styled-components': 'styled' }

First, we will run rollup to watch our src module and automatically recompile it into dist whenever we make changes.

$ npm start

The second part will be running the example create-react-app that’s linked to the local version of our module. In another tab:

$ cd example
$ npm start



Let’s start from the top of our components hierarchy. A lot of libraries requires width and height to specify size, but we will make it another way. We will require Wrapper component to be passed by props. And via refs, we will figure out the size of TimePicker. To handle changes in our user finger or mouse position we will add event handlers to Container component. Father in the updatePosition() function we will determine the new value that the user selected by computing mouse angle relative to the center of TimePicker. Also worth to mention that users of library pass theme props where he can specify some colors of the time picker. And since we are using styled-components we can set this theme in the root component and every child will be able to access it.

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components directory


The Circle component is a styled div tag. Here we can see how background color specified by accessing a theme.


In Minutes components we lay text evenly inside the circle by using some trigonometry. You may find getMinutes() little bit confusing, yet it simply returns an array of minutes [5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60]. Just always trying to keep immutability:)


Line component is an SVG line element. Here we also use sinuses and cosines:)


Start component is the button with the rocket. It placed absolutely in the center of the container. Also worth to mention that we need to handle onMouseDown() event here and call stopPropagation() because we don’t want this problem:)

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Don’t forget we also have an example project where we can import the TimePicker component.

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