implement a list with a static method javascript

Question

I must reimplement a list and the method forEach with the following instructions:

// Do not construct any array literal ([]) in your solution.

// Do not construct any arrays through new Array in your solution.

// DO not use any of the Array.prototype methods in your solution.

// You may use the destructuring and spreading (...) syntax from Iterable.

the result should look like:

const list = List.create(1, 2)
list.forEach((item) => console.log(item))

Here is my incomplete solution:

export class List {

  constuctor(){
    
  }

  public static create(...values: number[]): List {
    // Do *not* construct any array literal ([]) in your solution.
    // Do *not* construct any arrays through new Array in your solution.
    // DO *not* use any of the Array.prototype methods in your solution.

        // You may use the destructuring and spreading (...) syntax from Iterable.
        List list = new List();
        values.forEach(function(item){
          list.push(item);
        });  
        return list;
      }
    
      public forEach(callback: any){
        for (let i = 0; i<this.length ; i++){
           callback(this[i], i, this);
        }
      }
    
    }

in the create loop, but the problem, as a static method, the this is not recognized

EDITED thanks to comments

Answer 1

...this is not recognised

It is. But you have not given this any property. And this is because:

• constuctor should be written as constructor
• You need to define a push method (since you call it in create)
• You need to define a length property (since you reference it in forEach)

Furthermore, there some other issues:

• you write that Array.prototype functions cannot be used, but your code has values.forEach(), ... so that is a violation of that rule. Use a for..of loop instead.

Here is your code with those remarks taken on board:

class List {
  constructor() {
    this.length = 0;    
  }

  push(value) {
    this[this.length++] = value;
  }

  static create(...values) {
    let list = new List();
    for (let item of values) {
      list.push(item);
    }
    return list;
  }
    
  forEach(callback) {
    for (let i = 0; i < this.length ; i++) {
      callback(this[i], i, this);
    }
  }
}


const list = List.create(1, 2)
list.forEach((item) => console.log(item))

Remarks

The above "test" will be fine, but when also assignments to properties are to work correctly, like list[2] = 3, then there are more things to take care of. Take for instance this program:

const list = List.create(1, 2);
list[5] = 42; // should update length
list.check = true; // should not update length
console.log("length = " + list.length);
console.log("enumerable keys are " + Object.keys(list));
list.forEach((item) => console.log(item)); // should not output empty slots
list.length = 1; // should delete some index properties
list.forEach((item) => console.log(item)); // should not output deleted items

...then the output should be:

length = 6
enumerable keys are 0,1,5,check
1
2
42
1

You can make this happen by trapping the access to properties, and making length a getter/setter. But you'd also need to distinguish between properties that are array indices, and which are not, so all-in-all that would make the code less trivial.