Flatten javascript objects into a single-depth object

Flatten object

function flattenObj(obj, preKey) {
    const entries = Object.entries(obj);

    return entries.reduce((acc, curr) => {
        let [key, value] = curr;

        return typeof value !== 'object'
            ? Object.assign(acc, { [preKey ? `${preKey}.${key}` : key] : value })
            : Object.assign(acc, flattenObj(value, preKey ? `${preKey}.${key}` : key));
    }, {});
}

// Initial call do not pass preKey
// eg

console.log(
flattenObj({
    a: 20,
    b: 'hello',
    c: {
      p: "234"
    },
    p: {
      q: {
        r: {
          l: 12,
          m: 'rto'
        }
      }
    }
})
);

// output
// { a: 20, b: 'hello', 'c.p': '234', 'p.q.r.l': 12, 'p.q.r.m': 'rto' }