var a = { a: 'oh', b: 'my', d: 'ss' };

var b = { c: 'goddess', d: 's2s' };

var c = _.merge(a, b);

console.log('merge', c)

const mergeFunc = (obj, source) => {

  return obj ? obj : source;

};

​

var a = { a: 'oh', b: 'my', d: 'ss', non: "baseValue" };

var b = { c: 'goddess', d: 's2s', non: false, };

var c = _.mergeWith(a, b);

console.log('mergeWith', c, mergeFunc)