Javascript Create new Number wıth own properties-CodePudding

I want create new number object with own properties from Number. But when assign a number value to my variable, my variable turn to Number(primitive wrapper object).and loss own properties.How can I prevent this? Example

class Fnumber extends Number {
  value = 0;
  [Symbol.toPrimitive](hint) {
    if (hint === 'object') {
      return this;
    }
    return this.value;
  };
  //I don't want use Number.prototype.add method because this effect all Number values.
  add = function(...v) {
    this.value  = Array.prototype.slice.call(arguments).reduce((o, v) => o   v)
  }
}
var nmbr = new Fnumber();
nmbr.add(4, 2, 4);
console.log(nmbr); //return a Object
console.log(nmbr   4); //return 14 is number
nmbr = 14;
console.log(nmbr); //return not a Object its Primative number value
console.log(nmbr   4); //return 14 a number
nmbr.add(4, 2, 4); //raise error.

CodePudding user response：

When doing nmbr = 14 you assign 14 to nmbr, you are not changing the nmbr.value, you are overwriting the object. Instead call add and use nmbr.value when needed.

class Fnumber extends Number {
  value = 0;

  add(...v) {
    this.value  = Array.prototype.slice.call(arguments).reduce((o, v) => o   v)
  }
}
var nmbr = new Fnumber();
nmbr.add(4, 2, 4);
console.log(nmbr.value);
nmbr.add(5);
console.log(nmbr.value);

nmbr.value = 25; // assign a value to nmbr.value
console.log(nmbr.value);

If you are not planning on reassigning the object, a good practice is to use const instead of var, see the error below.

class Fnumber extends Number {};
const nmbr = new Fnumber();
nmbr = 14;

CodePudding user response：

I found the solution indirectly.

class Fnumber extends Number {
value = 0;
add(...v) {
   this.value  = Array.prototype.slice.call(arguments).reduce((o, v) => o   v)
}
}
//temğrary variable description
var _nmbr=new Fnumber();
//Define nmbr variable in global scobe
Object.defineProperty(window,"nmbr",{
    enumerable: true,
    configurable: true,
    get() { return _nmbr; },
    set(val) { if (typeof val=="number")_nmbr.value=val; }
});
nmbr=4;
console.log(nmbr 2);//output 6
//still nmbr variable is object,because assigned value  to _nmbr.value with above set method
nmbr.add(4, 2, 4);
console.log(nmbr 2);//output 16