Diff

Compares two objects and returns a structured summary of their differences.

Signature

Diff(object obj1, object obj2)

Parameters

• obj1 (object): The original object.
• obj2 (object): The updated object.

Returns

• object: An object with three properties:
  • added — properties present in obj2 but not in obj1 (values from obj2)
  • removed — properties present in obj1 but not in obj2 (values from obj1)
  • changed — properties in both but with different values, each as {from, to}

Description

Performs a shallow (top-level) comparison of two objects. Nested objects and arrays are compared using deep equality, but reported as atomic {from, to} pairs when they differ. To diff nested objects, call Diff again on the inner values.

Although at the type level, null is never equal to null, Diff() performs a semantic comparison of null values: two null values for the same key are treated as equal (no change reported).

When the two objects are identical, the result contains three empty objects: {added: {}, removed: {}, changed: {}}.

Examples

var old = {name: "Alice", age: 30, city: "NYC"}
var updated = {name: "Alice", age: 31, email: "a@b.com"}
var d = Diff(old, updated)
# d.added   = {email: "a@b.com"}
# d.removed = {city: "NYC"}
# d.changed = {age: {from: 30, to: 31}}

# Drill into nested changes
var s1 = {user: {name: "Alice", role: "admin"}}
var s2 = {user: {name: "Alice", role: "editor"}}
var d2 = Diff(s1.user, s2.user)
# d2.changed = {role: {from: "admin", to: "editor"}}