static js(entry, output) {
        assert(
            typeof entry === 'string' || Array.isArray(entry),
            'mix.js() is missing required parameter 1: entry'
        );

        assert(
            typeof output === 'string',
            'mix.js() is missing required parameter 2: output'
        );
    }
Assert that the call the mix.js() is valid.

@param {any} entry
@param {any} output