I have a JavaScript project that uses Webpack 4 with source maps:

```
mode: 'development',
entry: { app: './src/app.js' },
output: {
    filename: 'app.[contenthash].js',
    path: outputPath,
},
devtool: 'sourcemap',
externals,
.... 

```

It generates 2 JS files in my `dist` folder:
`app.[contenthash].js` and `app.[contenthash].js.map` attached to it.

I installed `source-map-explorer`:
<https://www.npmjs.com/package/source-map-explorer>

But when i run it on these files, i get the error:

> 
> Your source map refers to generated column 8 on line 17, but the
>  source only contains 0 column(s) on that line. Check that you are
>  using the correct source map.
> 
> 
> 

How can i fix that?

**EDIT:**

When i change Webpack's mode to `production` it's not throwing that error. Why?
Now with `production` mode, it just hangs when i run it.. how long does it suppose to take?