#506 Object.assign()

Implement your own version of Object.assign() that copies enumerable own properties from source objects to a target object. This is a fundamental JavaScript utility that powers the object spread operator under the hood.

Requirements

1. Property copying – Copy all enumerable own properties from sources to target
2. Multiple sources – Support variadic arguments with multiple source objects
3. Property overwriting – Later sources should override earlier properties
4. Return target – Return the modified target object (same reference)
5. Edge case handling – Handle null, undefined, and primitive sources gracefully

Key Behaviors

• Enumerable properties only – Skip non-enumerable and inherited properties
• Symbol properties – Copy symbol-keyed properties when enumerable
• Primitive sources – Ignore null, undefined, strings, numbers, booleans
• Property precedence – Later sources override earlier ones
• Reference preservation – Return the same target object reference

Example

const target = { a: 1 };
const source1 = { b: 2, c: 3 };
const source2 = { c: 4, d: 5 };

objectAssign(target, source1, source2);
// target is now { a: 1, b: 2, c: 4, d: 5 }
// Returns the same target object

objectAssign({}, { a: 1 }, null, undefined, { b: 2 });
// Returns { a: 1, b: 2 }

// Symbol properties
const symbol = Symbol('key');
objectAssign({}, { [symbol]: 'value', regular: 'prop' });
// Returns { regular: 'prop', [Symbol(key)]: 'value' }

Key Challenge

The function must properly iterate over enumerable own properties while handling edge cases like primitive sources and maintaining the correct property precedence order.