val-loader

Install

npm install val-loader --save-dev

Examples

If you have a module findAnswer.js like this:

function findAnswer() {
    return {
        code: 'module.exports = 42;'
    };
}

module.exports = findAnswer;

you can use the val-loader to generate source code on build time:

// webpack.config.js
module.exports = {
    ...
    module: {
        rules: [{
            test: require.resolve('path/to/findAnswer.js'),
            use: [{
                loader: 'val-loader'
            }]
        }]
    }
};

A complete example of all available features looks like this:

const ask = require('./ask.js');
const generateResult = require('./generateResult.js');

function findAnswer(options) {
    return ask(options.question)
        .then(generateResult)
        .then(result => ({

            code: result.code,
            sourceMap: result.sourceMap,
            ast: result.abstractSyntaxTree,

            // Mark dependencies of findAnswer().
            // The function will be re-executed if one of these
            // dependencies has changed in watch mode.
            dependencies: [
                // Array of absolute native paths!
                require.resolve('./ask.js'),
                require.resolve('./generateResult.js')
            ],

            // Flag the generated code as cacheable.
            // If none of the dependencies have changed,
            // the function won't be executed again.
            cacheable: true

        }));
}

module.exports = findAnswer;

// webpack.config.js
module.exports = {
    ...
    module: {
        rules: [{
            test: require.resolve('path/to/findAnswer.js'),
            use: [{
                loader: 'val-loader',
                options: {
                    question: 'What is the meaning of life?'
                }
            }]
        }]
    }
};

Usage

The module that is loaded with this loader must stick to the following interfaces:

Expected module interface

The loaded module must export a function as default export with the following function interface.

module.exports = function (...) { ... };

Modules transpiled by Babel are also supported.

export default function (...) { ... }

Expected function interface

The function will be called with the loader options and must either return:

• an object with the following object interface or
• a promise that resolves to the following object interface

Expected object interface

Loader Options

The val-loader itself has no options. The options are passed as they are (without cloning them) to the exported function.