[Javascript] Webpack Loaders, Source Maps, and ES6

Using ES6

---

To use ES6, we need loader.

1. Modify webpack.config.js file:

module.exports = {
    entry: './index.js',
    output: {
        filename: 'bundle.js',
        path: __dirname
    },
    module: {
        loaders: [
            {test: /\.js$/, loader: 'babel', exclude: '/node_modules/'}
        ]
    }
};

We add module property, which is an object. We define the loaders property here which is an array of objects.

• test: It is a regex, will include all the files which match the regex. In the exmaple, we say that "include all the js files".
• loader: You need to define the ES6 loader for this, which is 'babel'. For that, you need to install it by:

npm install babel-loader

• exclude: Tell which files you don't want to include.

　　2. Change file using ES6 style:

//lam-dom-binding.js

export default {
  bindEls(el1, el2){
    el1.addEventListener('keyup', () =>  el2.value = el1.value)
    el2.addEventListener('keyup', () =>  el1.value = el2.value)
  }
}

　　3. run: webpack --watch

Source map

---

One useful thing is see the source map (means see lam-dom-binding.js map to which part in the bundle.js). The reason it is useful is because when we open the devtool, we just saw a big bundle.js file:

which is not useful for debugging.

To enable the source map, we need to add one property in webpack.config.js:

module.exports = {
    entry: './index.js',
    output: {
        filename: 'bundle.js',
        path: __dirname
    },
    devtool: 'eval', //init compile fast, recompile also very fast
    module: {
        loaders: [
            {test: /\.js$/, loader: 'babel', exclude: '/node_modules/'}
        ]
    }
};

After that, run 'webpack --watch' again. We can see from the devtool, it show the 'webpack://'

But you can see that code is still ES5 style, if you want what you coded, instead of using 'eval', you can use 'eval-source-map'.

module.exports = {
    entry: './index.js',
    output: {
        filename: 'bundle.js',
        path: __dirname
    },
    devtool: 'eval-source-map',
    module: {
        loaders: [
            {test: /\.js$/, loader: 'babel', exclude: '/node_modules/'}
        ]
    }
};

This can a little bit longer time to compile, then you can see the code you just worte:

Both 'eval' and 'eval-source-map' are recommended using in dev time.

If you want to use in production code:

module.exports = {
    entry: './index.js',
    output: {
        filename: 'bundle.js',
        path: __dirname
    },
    devtool: 'source-map',
    module: {
        loaders: [
            {test: /\.js$/, loader: 'babel', exclude: '/node_modules/'}
        ]
    }
};

It will add a .map file for you. That file is not actually loaded into the browser until the DevTools are brought up.