isEqualWith

isEqualWith is a function in the lodash utility library that performs a deep equality comparison between two values while allowing a user-supplied customizer to influence or override the result. It extends the behavior of isEqual by enabling tailored comparisons for specific values or structures.

The function accepts three arguments: value, other, and customizer. It returns a boolean indicating whether the two inputs are considered equal. During the comparison, isEqualWith traverses objects and arrays recursively, checking nested properties and elements. When the customizer is provided, it is invoked for each pair of compared values (along with contextual information such as keys and parent objects). If the customizer returns a boolean, that value is used as the result for that comparison. If the customizer returns undefined, the default deep equality logic is applied for that pair.

isEqualWith preserves the deep and recursive nature of isEqual, including handling of circular references. This means that, in the absence of an override from the customizer, two complex structures with the same shape and values are considered equal. The customizer provides a hook to treat certain values differently—such as treating objects with a subset of properties as equal, or handling special cases like NaN or custom classes—according to the user’s domain rules.

In practice, isEqualWith is useful when exact structural equality is too rigid, and a controlled level of customization is desired. It is a specialized variant of lodash’s isEqual and is often paired with specific comparison logic to suit application-specific needs. See also: isEqual, isMatch, and lodash documentation on customizers.