FreeCodeCamp/HelpFrontEnd

Get help on our Front End Development projects.

Johnny

@JohnnyBizzel

Also -2 - 5 = ?

NaN

Some users have a (+-) button to change the number to a negative or positive.

(I didn't)

I just detected it in my code

siliconchild

@siliconchild

yeah a seperate +/- button seems easier to implement as -2+-5 seems challenging to implement as it gets confused with -2+-5 as just -2-5, like the user changed the operator

could you tell me about object literal vs singleton class

the answers i find online are too techincal

and beyond my current understanding

also about adding comments, does my comments make sense? is this the way to explain code or can you tell me what I'm doing wrong there

Johnny

@JohnnyBizzel

could you tell me about object literal vs singleton class

I was going to ask you! If you can explain it, it means you understand it.

Comments are great. You are a rare example to many coders who don't bother commenting!!

I would say some are not necessary (for me) but if you are in the habit of writing comments, stick at it!

siliconchild

@siliconchild

Thank You, From my understanding you use classes when you need to create multiple instances of an object, when you just need one and only one instant, a object literal with methods and a class with singleton functions seem similar in utility

I'm confused which is to use when

Johnny

@JohnnyBizzel

Object literals you see everywhere these days

Very useful

Singleton class I think means you can only have once instance of that class

This is used a lot these days with modules in node for example

So you get lots of plugins for node that add functionality to your code -

These should be imported once and from then on you refer to that one instance of the module.

siliconchild

@siliconchild

@JohnnyBizzel yes classes that has one instance, i believe. these classes don;t need to be instantiated and can be used like object literals

Johnny

@JohnnyBizzel

Yes - a good technique to learn

siliconchild

@siliconchild

@JohnnyBizzel sorry i didn't understand their difference, only that node modules seem to use singletons. can you tell me what makes sense in my code, is it object literals and if so why?

Johnny

@JohnnyBizzel

Not sure. I don't see a New anywhere

As in const x = new Calc

I think this is instantiating a class

siliconchild

@siliconchild

@JohnnyBizzel Since I used static functions inside the class, There is no need to create a new instance of the object like const x = new Calc, I can just use const x = Calc.operate() like i would if i was using a simple object literal with methods

this is what confuses me

Johnny

@JohnnyBizzel

Oh ok. I have done similar in C# but not JS.

This is probably the difference then.

Not sure. I would have to read up on it more.

Thanks :)

siliconchild

@siliconchild

From reading online I sort of think that object literals and singletons classes are essentially the same thing, just different ways of writing the same. But I cold be entirely wrong

Johnny

@JohnnyBizzel

@siliconchild Could be.

Aditya

@ezioda004

@siliconchild Semantically Object literals and Classes are different thing. Classes are literal syntactical sugar for:

function Car (name){
  this.name = name
}
Car.prototype.sound = function(){
  console.log("vroom");
}

// class syntax
class Car {
  constructor(name){
    this.name = name;
  }
  sound(){
    console.log("vroom");
  }
}

As I can see you have constructor() function but you arent instantiating the class, so shouldnt you use static class field instead?

A recent JS proposal is adding static fields to the class, I think it'd be better for your use case:

class Calc {
    static sum;
    static operatorMemory;

    static reset() {
        Calc.sum = undefined;
        Calc.operatorMemory = undefined;
    }
 ...

siliconchild

@siliconchild

I didn't knew about static variables, makes sense . Thank you

Aditya

@ezioda004

Note: that you'd have to use babel to transpile this.

Since its a stage 3 proposal and not a standard feature just yet.

siliconchild

@siliconchild

oh so i cannot use static sum just yet without relying on babel?

Aditya

@ezioda004

Sadly no, but its again just syntactic sugar for:

class Calc {
}
Calc.sum;
Calc.operatorMemory;

So you can still use this

siliconchild

@siliconchild

so i have to define the variables outside the class?

Aditya

@ezioda004

Correct.

siliconchild

@siliconchild

what i did only makes sense if need multiple instances of those variables? right?

Aditya

@ezioda004

You mean the constructor() method?

siliconchild

@siliconchild

yeah

Aditya

@ezioda004

Yeah that method is only executed if you instantiate a class like const x = new Calc()

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