DefinitelyTyped/types/fast-json-patch/fast-json-patch-tests.ts

import * as jsonpatch from 'fast-json-patch';

var myobj: {
  firstName: string,
  contactDetails: {
    phoneNumbers: string[]
  }
} = { firstName: "Albert", contactDetails: { phoneNumbers: [] } };
var patches: jsonpatch.Patch[] = [
  { op: "replace", path: "/firstName", value: "Joachim" },
  { op: "add", path: "/lastName", value: "Wester" },
  { op: "add", path: "/contactDetails/phoneNumbers/0", value: { number: "555-123" } }
];
jsonpatch.apply(myobj, patches);

var myobj2 = { firstName: "Joachim", lastName: "Wester", contactDetails: { phoneNumbers: [{ number: "555-123" }] } };
var observer = jsonpatch.observe(myobj2);
myobj2.firstName = "Albert";
myobj2.contactDetails.phoneNumbers[0].number = "123";
myobj2.contactDetails.phoneNumbers.push({ number: "456" });
var patches2 = jsonpatch.generate(observer);

var objA = { user: { firstName: "Albert", lastName: "Einstein" } };
var objB = { user: { firstName: "Albert", lastName: "Collins" } };
var diff = jsonpatch.compare(objA, objB);

var obj = { user: { firstName: "Albert" } };
var patches3 = [{ op: "replace", path: "/user/firstName", value: "Albert" }, { op: "replace", path: "/user/lastName", value: "Einstein" }];
var errors = jsonpatch.validate(patches, obj);
if (errors.length === 0) {
  //there are no errors!
} else {
  for (var i = 0; i < errors.length; i++) {
    if (!errors[i]) {
      console.log("Valid patch at index", i, patches[i]);
    } else {
      console.error("Invalid patch at index", i, errors[i], patches[i]);
    }
  }
}