JSFiddle - React, Tailwind, and code Playground

JavaScript

var upperCased = [
    { ID: 1, NAME: 'Fred' },
  { ID: 2, NAME: 'Sarah' },
    { ID: 3, NAME: 'Joe' },
];


var lowerCased = upperCased.map(function(item) {
    var mapped = {};
  for (var key in item) {
    mapped[key.toLowerCase()] = item[key];
  }

  return mapped;
});

console.log(lowerCased);