ValueOf

ValueOf is a term used to describe a method or function that retrieves a primitive or canonical value from an object or input. It appears in several programming languages, often with similar aims but different specifics.

In JavaScript, valueOf is a method on Object.prototype that returns the primitive value of the object. The default implementation for most objects returns the object itself, while primitive wrappers return the corresponding primitive value. During type coercion, JavaScript may call valueOf (and sometimes toString) to convert an object to a primitive. Objects can override valueOf to customize the coercion behavior; for example, an object with valueOf returning 3 will contribute a numeric value of 3 in arithmetic expressions.

In Java, valueOf appears as static factory methods on wrapper classes and on String. Examples include Integer.valueOf(int), Boolean.valueOf(boolean), and String.valueOf(Object). These methods return boxed wrapper objects or a string representation. The Integer, Boolean, and other wrappers often implement caching for small values (for instance, Integer.valueOf caches values in the range -128 to 127) to improve memory efficiency. String.valueOf(obj) returns "null" if the argument is null or obj.toString() otherwise, with overloads for primitive types.

The overarching idea is to provide a standard way to obtain a representative value from a given input, facilitating boxing, string conversion, or numeric operations. The exact behavior of valueOf depends on the language and the type involved, so consulting language-specific documentation is important.

See also: toString, boxing, primitive coercion, parse.