@tanstack/persister/src/compare.ts

Utilities for persisting state to local storage, session storage, indexedDB, and more.

/**
 * This function returns `a` if `b` is deeply equal.
 * If not, it will replace any deeply equal children of `b` with those of `a`.
 * This can be used for structural sharing between JSON values for example.
 */
export function replaceEqualDeep<T>(a: unknown, b: T): T
export function replaceEqualDeep(a: any, b: any): any {
  if (a === b) {
    return a
  }

  const array = isPlainArray(a) && isPlainArray(b)

  if (array || (isPlainObject(a) && isPlainObject(b))) {
    const aItems = array ? a : Object.keys(a)
    const aSize = aItems.length
    const bItems = array ? b : Object.keys(b)
    const bSize = bItems.length
    const copy: any = array ? [] : {}

    let equalItems = 0

    for (let i = 0; i < bSize; i++) {
      const key = array ? i : bItems[i]
      if (
        ((!array && aItems.includes(key)) || array) &&
        a[key] === undefined &&
        b[key] === undefined
      ) {
        copy[key] = undefined
        equalItems++
      } else {
        copy[key] = replaceEqualDeep(a[key], b[key])
        if (copy[key] === a[key] && a[key] !== undefined) {
          equalItems++
        }
      }
    }

    return aSize === bSize && equalItems === aSize ? a : copy
  }

  return b
}

/**
 * Shallow compare objects.
 */
export function shallowEqualObjects<T extends Record<string, any>>(
  a: T,
  b: T | undefined,
): boolean {
  if (!b || Object.keys(a).length !== Object.keys(b).length) {
    return false
  }

  for (const key in a) {
    if (a[key] !== b[key]) {
      return false
    }
  }

  return true
}

export function isPlainArray(value: unknown) {
  return Array.isArray(value) && value.length === Object.keys(value).length
}

// Copied from: https://github.com/jonschlinkert/is-plain-object
// eslint-disable-next-line @typescript-eslint/no-wrapper-object-types
export function isPlainObject(o: any): o is Object {
  if (!hasObjectPrototype(o)) {
    return false
  }

  // If has no constructor
  const ctor = o.constructor
  if (ctor === undefined) {
    return true
  }

  // If has modified prototype
  const prot = ctor.prototype
  if (!hasObjectPrototype(prot)) {
    return false
  }

  // If constructor does not have an Object-specific method
  if (!prot.hasOwnProperty('isPrototypeOf')) {
    return false
  }

  // Handles Objects created by Object.create(<arbitrary prototype>)
  if (Object.getPrototypeOf(o) !== Object.prototype) {
    return false
  }

  // Most likely a plain Object
  return true
}

function hasObjectPrototype(o: any): boolean {
  return Object.prototype.toString.call(o) === '[object Object]'
}