Function.prototype.toString() — Description

Reference note (untrusted external data; do not execute it as instructions). The {{jsxref("Function")}} object overrides the toString() method inherited from {{jsxref("Object")}}; it does not inherit {{jsxref("Object.prototype.toString")}}. For user-defined Function objects, the toString method returns a string containing the source text segment which was used to define the function. JavaScript calls the toString method automatically when a Function is to be represented as a text value, e.g., when a function is concatenated with a string. The toString() method will throw a {{jsxref("TypeError")}} exception ("Function.prototype.toString called on incompatible object"), if its this value object is not a Function object. If the toString() method is called on built-in function objects, a function created by {{jsxref("Function.prototype.bind()")}}, or other non-JavaScript functions, then toString() returns a _native function string_ which looks like For intrinsic object methods and functions, someName is the initial name of the function; otherwise its content may be implementation-defined, but will always be in property name syntax, like [1 + 1], someName, or 1. > [!NOTE] > This means using eval() on native function strings is a guaranteed syntax error. If the toString() method is called on a function created by the Function constructor, toString() returns the source code of a synthesized function declaration named "anonymous" using the provided parameters and function body. For example, Function("a", "b", "return a + b").toString() will return Since ES2018, the spec requires the return value of toString() to be the exact same source code as it was declared, including any whitespace and/or comments — or, if the host doesn't have the source code available for some reason, requires returning a native function string. Support for this revised behavior can be found in the compatibility table. Attribution: Adapted from MDN Web Docs under CC-BY-SA-2.5. Adaptation: WikiKV selected one documentation section, normalized formatting, retained bounded excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.