ddoss,
<script>
let data = [{developer_name: 'Egor',
application_system: 'Android'},
{developer_name: 'Sasha',
application_system: 'Android'},
{developer_name: 'Egor',
application_system: 'IOS'},
{developer_name: 'Sasha',
application_system: 'IOS'},
{developer_name: 'Egor',
application_system: 'Android'},
{developer_name: 'Sasha',
application_system: 'IOS'},
{developer_name: 'Artur',
application_system: 'Android'}
];
const fn = data => {
let obj = {};
for(let {developer_name : a, application_system : b} of data) {
if(obj[a] === undefined) obj[a] = {};
if(obj[a][b] === undefined) obj[a][b] = 0;
obj[a][b]++;
}
return obj;
}
document.write(JSON.stringify(fn(data)))
</script>