axios transformRequest - how to alter JSON payload

Question

I am using axios in my Express API and I want to transform the payload before sending it off to another API. axios has just the thing for this called transformRequest. This

Answer 1

To amend the values instead of override the output in the request I would do this:

const instance = axios.create({
baseURL: 'api-url.com',
transformRequest: [
    (data, headers) => {
        data.append('myKey','myValue');            
        return data;
    },
]
});