JSFiddle - React, Tailwind, and code Playground
JavaScript
var obj = {TempPoints: "{'lat': 51.478,'lng': -3.192},{'lat': 51.478,'lng': -3.192},{'lat': 51.47840998047034,'lng': -3.1926937697490536}"};
var obj = "["+obj.TempPoints+"]";
var newObj = eval(obj);
console.log(newObj); //It's an array of Objects