Querying for a specific item type within a document in Sanity.io

/**
 * Use to check for link 'url' properties that have been migrated incorrectly.
 * Run this script with: `sanity exec --with-user-token scripts/migrate/patchLink.ts`
 */

 import sanityClient from 'part:@sanity/base/client';
 import consola from 'consola';
 
 const client = sanityClient.withConfig({
   dataset: 'dev',
   apiVersion: 'v2020-03-15',
 });
 
 const patchDocument = (obj, updateDocument) => {
   if (obj !== null) {
     Object.entries(obj).forEach(([key, value]) => {
       // find the _type you're looking for
       if (key === '_type' && value === 'link') {
         // do what you need to to the data of that object 
         if (obj.url) {
           if (!obj.href) {
             obj.href = obj.url;
           }

           delete obj.url;

           updateDocument = true;
         }
       } else if (typeof value === 'object') {
         updateDocument = patchDocument(value, updateDocument);
       }
     });
   }
 
   return updateDocument;
 };
 
 const runProcess = async () => {
   const allDocuments = await client.fetch(`*[]`);
 
   let documentsUpdated = 0;
   const concurrency = 50; // keep under sanity rate limit
 
   console.time('patchLink');
 
   while (allDocuments.length) {
     await Promise.all(
       allDocuments.splice(0, concurrency).map(async doc => {
         const updateDocument = patchDocument(doc, false);
 
         if (updateDocument) {
           const docTitle =
             (doc._type == 'profile' && `${doc.firstName} ${doc.lastName}`) || doc.title?.en_GB || doc.title || doc._id;
           consola.success(`Fixing (${doc._type}) ${docTitle}`);
 
           await client.createOrReplace(doc);
 
           documentsUpdated++;
         }
       })
     );
   }
 
   <http://consola.info|consola.info>(`Number of documents updated: ${documentsUpdated}`);
   console.timeEnd('patchLink');
 };
 
 runProcess();