I am getting Invalid configuration error like this

[webpack-cli] Invalid configuration object. Webpack has been 
initialized using a configuration object that does not match the API schema.
 - configuration.entry['/js/app'] should not contain the item 
'project/resources/sass/app.scss' twice.
   -> All modules are loaded upon startup. The last one is exported.

Here is my webpack.mix.js

const mix = require('laravel-mix');

mix.js('resources/js/app.js', 'public/js').vue()
.sass('resources/sass/app.scss', 'public/css')


mix.js('resources/js/app.js', 'public/js').react()
    .sass('resources/sass/app.scss', 'public/css');

I am configuring this first time. so I have no idea what I am doing it wrong. Please help me understand this issue.

Let me know if I need to add more file to understand this problem like package.json