Remove duplicate values from an object array with an accessor function to identify dupes

uniq.js

/** Example 1: uniq([
    {name:'John',id:1},
    {name:'Jane',id:2},
    {name:'John',id:3},
    {name:'Jack',id:4}
   ],e=>e.name)= [
    {name:'John',id:3},
    {name:'Jane',id:2},
    {name:'Jack',id:4}
   ]
 Example 2: uniq([
    {name:'John',id:1},
    {name:'Jane',id:2},
    {name:'John',id:3},
    {name:'Jack',id:4}
  ],e=>e.name,true)=[
    {name:'John',id:1},
    {name:'Jane',id:2},
    {name:'Jack',id:4}
 ] **/
let uniq=(objArr,fn,useFirst)=>Object.values(objArr.reduce((collector,obj)=>{
  let key=fn(obj);
  if(!useFirst || !collector[key])
    collector[fn(obj)]=obj;
  return collector},
  {})
)