Cloning and comparing values

JavaScript's === compares objects and arrays by reference, and Object.assign only copies top-level properties. Lodash gives you explicit control over both comparison depth and copy depth.

Compare by value, not by reference

_.isEqual performs a deep comparison and returns true when two values are structurally equivalent, even if they are different object instances:

var a = { x: 1, nested: { y: 2 } };
var b = { x: 1, nested: { y: 2 } };

a === b;
// => false

_.isEqual(a, b);
// => true

_.isEqual supports arrays, array-like objects, plain objects, Date, RegExp, Map, Set, and typed arrays. Function values and non-enumerable properties are not compared.

Custom comparisons

Pass a customizer to _.isEqualWith when you need a comparison rule isEqual doesn't provide:

function isGreeting(value) {
  return /^h(?:i|ello)$/.test(value);
}

function customizer(objValue, othValue) {
  if (isGreeting(objValue) && isGreeting(othValue)) {
    return true;
  }
  // returning undefined falls back to the default comparison
}

_.isEqualWith(['hello', 'goodbye'], ['hi', 'goodbye'], customizer);
// => true

Choose a clone depth

_.clone copies only the top level of an object or array; nested objects are shared by reference with the original. cloneDeep recursively clones every nested value, so the copy is fully independent.

var original = { x: 1, nested: { y: 2 } };

var shallow = _.clone(original);
var deep = _.cloneDeep(original);

shallow.nested === original.nested;
// => true — mutating shallow.nested also changes original.nested

deep.nested === original.nested;
// => false — mutating deep.nested leaves original.nested untouched

Use _.cloneDeepWith when part of the structure needs custom copy logic — for example, values cloneDeep cannot represent, such as DOM nodes or class instances with private state.

Related methods

Next steps

• See every type-checking method — isPlainObject, isNil, isArrayLike, and more — in Lang methods.
• Merging deeply nested objects has its own rules; see merge and mergeWith in the Object reference.