JSFiddle - React, Tailwind, and code Playground

JavaScript

var arrayBefore = [
  {"name":"Alan","height":"171","weight":"66"},
  {"name":"Ben","height":"182","weight":"90"}
 ];

var arrayAfter= [
  {"name":"Alan","height":"171","weight":"66"},
  {"name":"Ben","height":"182","weight":"90"},
  {"name":"Chris","height":"163","weight":"71"}
 ];

//Get a list of all the names in the before array
var beforeNames = arrayBefore.map(function(person) { return person.name });

//Filter the after array to only contain names not contained in the before array
var uniqueObjects = arrayAfter.filter(function(person) {
    return beforeNames.indexOf(person.name) === -1;
});

console.log(uniqueObjects); //{"name":"Chris","height":"163","weight":"71"