Finds diff between objects

object-diff.ts

type Change<T> = {
  path: Array<string>
  right: T
  left: T
}

function isPrimitive(value: any): boolean {
  const type = typeof value
  return ['number', 'date', 'boolean', 'string'].indexOf(type) > -1
}

function change<T>(path: Array<string>, a: T, b: T): Change<T> {
  return {
    path,
    left: a,
    right: b
  }
}

function arrToDict<T>(t: Array<T>): { [key: number]: T } {
  const obj: any = {}
  for (let i = 0; i < t.length; i++) obj[i] = t[i]
  return obj
}

function diffAB<T extends any>(a: T, b: T, path: string[]): Array<Change<T>> {
  let changes: Array<Change<any>> = []
  for (let i in a) {
    if (a.hasOwnProperty(i)) {
      if (b.hasOwnProperty(i)) {
        changes = changes.concat(diff(a[i], b[i], [...path, i]))
      } else {
        changes = changes.concat([change([...path, i], a[i], b[i])])
      }
    }
  }

  for (let i in b) {
    if (b.hasOwnProperty(i)) {
      if (!a.hasOwnProperty(i)) {
        changes = changes.concat([change([...path, i], a[i], b[i])])
      }
    }
  }
  return changes
}

function diff(a: any, b: any, path: Array<string> = []): Array<Change<any>> {
  if (a === b) return []
  // primitive check
  if (
    (isPrimitive(a) && !isPrimitive(b)) ||
    (!isPrimitive(a) && isPrimitive(b)) ||
    (isPrimitive(a) && isPrimitive(b) && a !== b)
  )
    return [change(path, a, b)]
  if (Array.isArray(a) && Array.isArray(b))
    return diffAB(arrToDict(a), arrToDict(b), path)

  return diffAB(a, b, path)
}