Notice that you can use the dns.promises.resolve function: https://nodejs.org/api/dns.html#dns_dnspromises_resolve_hostname_rrtype

so you would change your code to:

const rrtypes = ["A", "MX", "CNAME", "NS", "TXT"];

export const getAllRecords = async (req, res) => {
  const { domain } = req.params;

  // Notice that resData should be local to this function
  let resData = [];
  for (const rrtype of rrtypes) {
    try {
      const records = await dns.promises.resolve(domain, rrtype);
      resData.push(rrtype + " " + records);
      // IMO this would be better: resData.push({ type: rrtype, value: records });
    } catch (err) {
      // Log the error here
    }
  }

  res.send(resData);
};

The problem lies in your use of await. await should be used when calling async functions. At the moment you are using it when instantiating variables from an array.

Thanks to a comment by slebetman I was able to see this dns.resolve does not return a promise but uses callbacks to manage the async calls. As he also suggested we can fix this by creating a promise to manage these callbacks.

const rrtypes= ["A","MX","CNAME","NS","TXT"];
var resData = [];

const dnsResolvePromise = (domain, rrtype) => {
  return new Promise((resolve, reject) => {
    dns.resolve(domain, rrtype, (err, records) => { 
        if(err) return reject(err);
        resolve(rrtype+" "+records);
    });
  })
}

export const getAllRecords = async (req,res) => {
    const {domain} = req.params;
    for(const rrtype of rrtypes){
        try{
            const records = await dnsResolvePromise(domain, rrtype);
            resData.push(records);
       } catch (e){
         // Handle error
       }
    }    
    res.send(resData);
    resData = [];      
}