(to use it, copy and paste from 📁 module file： typeName())
// ⭐️ content of function definition (string)
function functionDefinition(value) {
// ---------------------------------------------------------------------
// ⭐️ will throw a TypeError if value is not a function:
// ⛔ TypeError:
// Function.prototype.toString requires that 'this' be a Function
// ---------------------------------------------------------------------
return Function.prototype.toString.call(value);
}