Function merge

Merges the properties of the source object into the target object.

This function performs a deep merge, meaning nested objects and arrays are merged recursively. If a property in the source object is an array or an object and the corresponding property in the target object is also an array or object, they will be merged. If a property in the source object is undefined, it will not overwrite a defined property in the target object.

Note that this function mutates the target object.

const target = { a: 1, b: { x: 1, y: 2 } };
const source = { b: { y: 3, z: 4 }, c: 5 };

const result = merge(target, source);
console.log(result);
// Output: { a: 1, b: { x: 1, y: 3, z: 4 }, c: 5 }
Copy

const target = { a: [1, 2], b: { x: 1 } };
const source = { a: [3], b: { y: 2 } };

const result = merge(target, source);
console.log(result);
// Output: { a: [3, 2], b: { x: 1, y: 2 } }
Copy

const target = { a: null };
const source = { a: [1, 2, 3] };

const result = merge(target, source);
console.log(result);
// Output: { a: [1, 2, 3] }
Copy