not all build output files will be overwritten, only files that contain modified parts of the code will be overwritten. You can inject hash into the filename of the build output, and you'll see. Please refer to the following code:

output: {
    filename: '[name].[hash].js'
}

that's inevitable, but overwriting is not a full update, it's just a local update. If there are no changes to the file, hash will not change.