Change value aggregation, if condition node js

How to change aggragte value in node js - mongodb

i have $project :

        $project : {
            type: '$data.type',
        }

and it give me output :

'type' : [
'bold',
'bold',
'regular',
'bold',
'regular'
]

the i want to change the output

if bold, then thick, else thin

i have try to use $cond and $switch, but idk why the i get just 1 output and that's default output

type: {
                        $switch : {
                            branches : [ 
                                {
                                case : { $eq : ['$data.type', 'bold']}, then: 'thick'
                                },
                                {
                                case : { $eq : ['$data.type', 'regular']}, then: 'thin'
                                },
                            ],
                            
                            default: ""
                        }
                    },

output :

"type": "",

can u all help me to solve this ? i have trying the $cond $eq too, but the output still default output

thank you for helping guys