Add front-end assets

The tutorials introduced a few basic approaches to building a front-end user interface for your projects. For example, the tutorials demonstrated:

Using Candid as a bare-bones interface to expose and test the functions in a canister.
Using raw JavaScript to display a simple pop-up alert window.
Using React and compiled JavaScript to embed HTML attributes and elements directly in a page.
Using React and TypeScript to import CSS properties from an external file.

This section takes a closer look at the default front-end template, front-end configuration options, and using other frameworks to build the user interface for your projects.

How the default template is used

As you might have noticed in the tutorials, projects include a template webpack.config.js file by default. Because webpack is a popular and highly-configurable module bundler for JavaScript-based applications, the default webpack.config.js file makes it easy to add the specific modules—such as react and markdown—that you want to use.

By default, the template webpack.config.js file also creates canister aliases based on the entries in the project’s dfx.json file. If you review the code in the template webpack.config.js file, you see that it performs this alias creation task using the following code block:

// List of all aliases for canisters. This creates the module alias for
// the `import ... from "ic:canisters/xyz"` where xyz is the name of a
// canister.
const aliases = Object.entries(dfxJson.canisters)
    .filter(([name,value]) => value.main)
    .reduce((acc, [name,value]) => {
  const outputRoot = path.join(__dirname, dfxJson.defaults.build.output, name);
  const filename = path.basename(value.main, ".mo");
  return {
    ...acc,
    ["ic:canisters/" + name]: path.join(outputRoot, filename + ".js"),
    ["ic:idl/" + name]: path.join(outputRoot, filename + ".did.js"),
  };
}, {});

Entry and output configuration

After creating canister aliases, the template webpack.config.js file generates a webpack configuration that adds the canister aliases automatically as imported modules in the default front-end entry point defined in the project’s dfx.json file. For example, using the default settings an import similar to the following is added to the src/CANISTER_assets/public/index.js file:

import CANISTER-ALIAS from 'ic:canisters/CANISTER-ALIAS';

Ensuring node is available in a project

Because projects rely on webpack to provide the framework for the default front-end, you must have node.js installed in your development environment and accessible in the project directory.

If you want to develop your project without using the default webpack configuration and canister aliases, you can remove the assets canister from the dfx.json file or build your project using a specific canister name. For example, you can choose to build only the hello program without front-end assets by running the following command:
```
dfx build hello
```
If you are using the default webpack configuration and running dfx build fails, you should try running npm install in the project directory then re-running dfx build.
If running npm install in the project directory doesn’t fix the issue, you should check the configuration of the webpack.config.js file for syntax errors.

Using other modules with the React framework

Several tutorials and sample projects in the examples repository illustrate how to add React modules using the npm install command. You can use these modules to construct the user interface components you want to use in your project. For example, you might run the following command to install the react-router module:

npm install --save react react-router-dom

You could then use the module to construct a navigation component similar to the following:

import React from 'react';
import { NavLink } from 'react-router-dom';

const Navigation = () => {
  return (
    <nav className="main-nav">
      <ul>
        <li><NavLink to="/myphotos">Remember</NavLink></li>
        <li><NavLink to="/myvids">Watch</NavLink></li>
        <li><NavLink to="/audio">Listen</NavLink></li>
        <li><NavLink to="/articles">Read</NavLink></li>
        <li><NavLink to="/contribute">Write</NavLink></li>
      </ul>
    </nav>
  );
}

export default Navigation;