Warning: The "to" argument must be of type string.

Setup:

• Windows 10
• Node v10.15.3
• npm 6.4.1
• yarn 1.16.0
• grunt 1.0.4

Gruntfile.js

module.exports = function(grunt) {
   require('load-grunt-tasks')(grunt);

   grunt.initConfig({

    babel: {
         dist: {
            files: {
               'js/app.js': 'js/app-compiled.js'
            }
         }
      },
   });

   grunt.registerTask("build", ["babel",]);
}

When i enter “grunt build” i receive respond: Warning: The "to" argument must be of type string. Received type undefined Use --force to continue. and only this. What is a “to” argument and why it isn’t be of type string? After all this is taken from the example and does not work.

[mread1208]

I believe the error you’re getting is that Babel cannot compile fileA.js into fileB.js because fileA.js doesn’t exist.

In the files object of the config, the key should be the output file name and the value should be the name of the file you want converted (seems backwards, but it makes sense if you look at it this way).

So in your example:

files: {
    'js/app.js': 'js/app-compiled.js'
}

You’re trying to convert a file called js/app-compiled.js into js/app.js. I believe you have these backwards, you should have a file called js/app.js and you want grunt / babel to compile that into a new file called js/app-compiled.js. Update your config to look like this and make sure you have a file called app.js in the correct location:

files: {
    'js/app-compiled.js': 'js/app.js'
}

[jgarite]

@RiddickAbaddon I’m not sure if you realized it already, but i realized it shortly after i posted here. The source file was not created. In my case, I was using concat first and the output from concat didnt create a file. therefore, babel didn’t find any file to work with. not sure if this is the same issue you have, but once i had the file in place, everything went fine.