TypeError: Cannot read properties of undefined (reading 'a')-CodePudding

I was trying classes and the this keyword in Javascript,and I wrote this code:

class p{
  constructor(p,a){
      p = p.p;
      a = p.a;
  };
};
const c = new p(p="1st aspect",a="2nd aspect");
console.log(this.c);

And I got this Error:

Cannot read properties of undefined (reading 'a')

I don't know whether this is compatible with classes or whether I passed in the wrong arguments,can someone help me there?

CodePudding user response：

The syntax for creating a class is wrong. You don't need to pass the parameter names. Just use

const c = new p("1st aspect","2nd aspect");

And it is not good practice to use lowercased frist letter as class name. Use P instead of p. And this.c is wrong. Just print

console.log(c);

CodePudding user response：

It's just the syntax you're using to create a class instance isn't correct in terms of attempting to use provided argument names ("p =", "a ="), and there may be some errors in your class construction. I think you may have been trying to do something like this:

class p {
  // These are ordered arguments, not named arguments 
  constructor(p,a) {
      // Save the value of p and a on the class instance
      this.p = p;
      this.a = a;
  };
};
// Create a new p class instance with the arguments in order
const classInstance = new p("1st aspect", "2nd aspect");

CodePudding user response：

Code should look like this

class P {
  constructor(p, a){
      this.p = p;
      this.a = a;
  };
};


const c = new P("1st aspect", "2nd aspect");
console.log(c); // <- just print c

I can see you're mixing some concepts and getting confused, I'd suggest you to read official MDN Docs, you'll learn about classes step by step.

As an extra, you'll notice that class names are named using PascalCase. This is because by following the naming convention you'll read and understand other people's code much faster (and even yours).

Hope this helped!