function function2string( fcn ) {
	return fcn2str.call( fcn );
}
Returns a string representing the source code of a provided function.

## Notes

-   If called on built-in functions, functions created by `Function.prototype.bind()`, or other non-JavaScript functions, the function returns a "native" function string similar to the following:

    ```text
    "function foo() { [native code] }"
    ```

    For intrinsic object methods and functions, `foo` is the initial name of the function.

-   If called on a function created by the `Function` constructor, the function returns the source code of a synthesized function declaration having the name "anonymous" and using the provided parameters and function body.

-   Starting in ES2018, the ECMAScript specification requires that the returned string contain the exact same source code as it was declared, including any whitespace and/or comments. If the host is unable to access the source code, the specification requires that the returned string be the native function string.

@param {Function} fcn - input function
@throws {TypeError} must provide a function
@returns {string} string representing function source code

@example
function add( x, y ) {
    return x + y;
}

var str = function2string( add );
// e.g., returns 'function add( x, y ) {\n    return x + y;\n}'