[рони]

misha.korolcov,

<script>
const grop = [
    { name: 'merseded', groupName: 'avto', idParent: '11' },
    {name: 'bmv', groupName: 'avto', idParent: '20' }
   ];
const city = [{name: 'test1', idMain: '11'},
              {name: 'test2', idMain: '11'},
              {name: 'test3', idMain: '20'},
              {name: 'test4', idMain: '11'}];


const resaltCity = grop.map(obj => (obj.children = city.filter(({idMain}) => idMain == obj.idParent), obj));

document.write(`<pre>${JSON.stringify(resaltCity, "", 4)}</pre>`)
    </script>

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