JSFiddle - React, Tailwind, and code Playground

JavaScript

var existing = ["562fae5a626ca2e032947baa"];
var newArr = [ { _id: '562fae5a626ca2e032947baa' },
      { _id: '562fae57626ca2e032947ba9' } ];

newArr = newArr.filter(function(val){
    return existing.indexOf(val) == -1;
});

console.log(newArr);