JSFiddle - React, Tailwind, and code Playground

JavaScript

var a = [
  { userId:"p1", item:1},
  { userId:"p2", item:2},
  { userId:"p3", item:4}
];

var b = [
  { userId:"p1", profile:1},
  { userId:"p2", profile:2}
];

a.forEach(function(aitem){
	b.forEach(function(bitem){
  	if(aitem.userId === bitem.userId){
    	_.assign(aitem, bitem)
    }
  })
});

console.log(a);