JSFiddle - React, Tailwind, and code Playground

JavaScript

var a = "{gallery: 'gal', smallimage: '/uploads/photo/image/3256/big_1303-1.jpg', largeimage: '/uploads/photo/image/3256/zoom_1303-1.jpg'}";

var jsontemp = a.replace((/([\w]+)(:)/g), "\"$1\"$2");
var correctjson = jsontemp.replace((/'/g), "\"");

var obj = JSON.parse(correctjson);

var c = obj.largeimage;

alert(c);