Core Operations

/**
 * Apply a full JSON Patch array on a JSON document.
 * Returns the {newDocument, result} of the patch.
 * @param document The document to patch
 * @param patch The patch array to apply
 * @param validateOperation false for no validation, true for default validation, or custom validator function
 * @param mutateDocument Whether to mutate the original document or clone it before applying
 * @param banPrototypeModifications Whether to ban modifications to __proto__, defaults to true
 * @returns Array of operation results with newDocument property
 */
function applyPatch<T>(
  document: T,
  patch: ReadonlyArray<Operation>,
  validateOperation?: boolean | Validator<T>,
  mutateDocument?: boolean,
  banPrototypeModifications?: boolean
): PatchResult<T>;

import { applyPatch } from "fast-json-patch";

const document = { name: "John", age: 30, hobbies: ["reading"] };
const patch = [
  { op: "replace", path: "/name", value: "Jane" },
  { op: "add", path: "/email", value: "jane@example.com" },
  { op: "add", path: "/hobbies/1", value: "swimming" }
];

// Apply with validation
const result = applyPatch(document, patch, true);
console.log(result.newDocument);
// { name: "Jane", age: 30, hobbies: ["reading", "swimming"], email: "jane@example.com" }

// Apply without mutating original
const result2 = applyPatch(document, patch, false, false);
// document remains unchanged, result2.newDocument contains the updated version

/**
 * Apply a single JSON Patch Operation on a JSON document.
 * Returns the {newDocument, result} of the operation.
 * @param document The document to patch
 * @param operation The operation to apply
 * @param validateOperation false for no validation, true for default validation, or custom validator function
 * @param mutateDocument Whether to mutate the original document or clone it before applying
 * @param banPrototypeModifications Whether to ban modifications to __proto__, defaults to true
 * @param index Operation index for error reporting
 * @returns Operation result with newDocument, and optionally removed value or test result
 */
function applyOperation<T>(
  document: T,
  operation: Operation,
  validateOperation?: boolean | Validator<T>,
  mutateDocument?: boolean,
  banPrototypeModifications?: boolean,
  index?: number
): OperationResult<T>;

import { applyOperation } from "fast-json-patch";

const document = { users: [{ name: "Alice" }] };

// Add operation
const addResult = applyOperation(document, {
  op: "add",
  path: "/users/1",
  value: { name: "Bob" }
});

// Remove operation
const removeResult = applyOperation(document, {
  op: "remove",
  path: "/users/0"
});
console.log(removeResult.removed); // { name: "Alice" }

// Test operation
const testResult = applyOperation(document, {
  op: "test",
  path: "/users/0/name",
  value: "Alice"
});
console.log(testResult.test); // true

/**
 * Apply a single JSON Patch Operation on a JSON document.
 * Returns the updated document. Suitable as a reducer.
 * @param document The document to patch
 * @param operation The operation to apply
 * @param index Operation index for error reporting
 * @returns The updated document
 */
function applyReducer<T>(document: T, operation: Operation, index: number): T;

import { applyReducer } from "fast-json-patch";

const document = { counter: 0 };
const operations = [
  { op: "replace", path: "/counter", value: 1 },
  { op: "add", path: "/status", value: "active" }
];

// Use as reducer
const result = operations.reduce(applyReducer, document);
console.log(result); // { counter: 1, status: "active" }

/**
 * Retrieves a value from a JSON document by a JSON pointer.
 * Returns the value.
 * @param document The document to get the value from
 * @param pointer An escaped JSON pointer
 * @returns The retrieved value
 */
function getValueByPointer(document: any, pointer: string): any;

import { getValueByPointer } from "fast-json-patch";

const document = {
  users: [
    { name: "Alice", profile: { age: 25 } },
    { name: "Bob", profile: { age: 30 } }
  ]
};

// Get nested values
const name = getValueByPointer(document, "/users/0/name"); // "Alice"
const age = getValueByPointer(document, "/users/1/profile/age"); // 30
const users = getValueByPointer(document, "/users"); // entire users array
const root = getValueByPointer(document, ""); // entire document

interface BaseOperation {
  path: string;
}

interface AddOperation<T> extends BaseOperation {
  op: 'add';
  value: T;
}

interface RemoveOperation extends BaseOperation {
  op: 'remove';
}

interface ReplaceOperation<T> extends BaseOperation {
  op: 'replace';
  value: T;
}

interface MoveOperation extends BaseOperation {
  op: 'move';
  from: string;
}

interface CopyOperation extends BaseOperation {
  op: 'copy';
  from: string;
}

interface TestOperation<T> extends BaseOperation {
  op: 'test';
  value: T;
}

interface OperationResult<T> {
  /** The removed value (for remove, replace, move operations) */
  removed?: any;
  /** Test result (for test operations) */
  test?: boolean;
  /** The updated document */
  newDocument: T;
}

interface PatchResult<T> extends Array<OperationResult<T>> {
  /** The final updated document after all operations */
  newDocument: T;
}