调用 function 时的返回值 object

Question

I'm creating a specific class in which I'd like to return the value of the class when it is called standalone, rather than returning the entire class model.

I've seen other people ask similar questions and seen recommended solutions using the valueOf and toString methods, but those methods both require writing the class as a string somewhere or calling it in some form of computation. I'd like my class to work in such a way where when I call the class, even in a simple console log by itself, it returns its value, without any other details about the other properties and methods available. I'm sure some people will say this is counterintuitive and probably not a good idea, but this is my ideal use case, and this is exactly how the Date() object works, so I feel this must be possible somehow.

When you create a new instance of the Date object, there are plenty of methods available (eg getMonth(), getFullYear(), setTime(), toJSON(), toDateString(), etc. ), but if you just call an instance of the date object without any methods or properties specified, it appears to return the date, unless this is just the browser console assisting developers by displaying some form of the stringified date, so they don't need to call .toString() to get the string value by default.

 const now = new Date(); console.log(now); // -> "2021-04-26T14:44:30.466Z" console.log(now.toString()); // -> Mon Apr 26 2021 10:44:59 GMT-0400 (Eastern Daylight Time) console.log(now.valueOf()); // -> 1619448336448

Would returning a "default" property like this be possible? Please keep in mind, I have already read similar questions here on StackOverflow and really scoured the platform and not seen any that answer this questions specifically.

Answer 1

The bottom line is that you don't have much control over what the console API does. When you hand it an object, in order to be helpful it will give you the object contents to explore. Of course the console code is familiar with native JavaScript types, so it might do something special with things like Date instances because, again, it's trying to be helpful. (That "helpfulness" causes a lot of confusion and there are hundreds if not thousands of questions here that can be traced to people not understanding what the console is trying to do.)

So you can add .toString() and .valueOf() methods to your classes, and take advantage of them for debugging etc. by either calling the methods explicitly or using them implicitly, as in:

console.log("Current status: " + myObject);

The + concatenation operator will implicitly call the .toString() method.