我试图从 ES 类参数创建一个数组，但我得到一个空数组，为什么？

Question

Consider this code for this scenario of creating an Array with value of "sideLength" and for "sides" times within this ES class, but I'm keep getting an empty array!! here is codepen link

class ShapeNew {
  constructor(name, sides, sideLength) {
    this.name = name;
    this.sides = sides;
    this.sideLength = sideLength;
  }
  tryArray() {
    let sides_array = [];
    for (let i = 0; i < this.sides; i++) {
      sides_array = sides_array.push(this.sideLength);
    }
    return sides_array;
  }
  newPerimeter() {
    let peri = this.tryArray();
    console.log(peri.reduce((sum, accum) => sum + accum));
  }
}
let new_square = new ShapeNew("square", 4, 5);
new_square.newPerimeter();

All I'm trying to do is convert 4 into [5,5,5,5], how do I do that?

Thanks in advance for looking into this, I appreciate it :)

Answer 1

You want this

sides_array.push(this.sideLength);

Not this

sides_array = sides_array.push(this.sideLength);

Because Array.push() does not return anything.

Answer 2

You are assigning to the variable sides_array the returned value of pushing a new element which is the new length, instead just push the element each time

 class ShapeNew { constructor(name, sides, sideLength) { this.name = name; this.sides = sides; this.sideLength = sideLength; } tryArray() { let sides_array = []; for (let i = 0; i < this.sides; i++) { sides_array.push(this.sideLength); } return sides_array; } newPerimeter() { let peri = this.tryArray(); console.log(peri.reduce((sum, accum) => sum + accum)); } } let new_square = new ShapeNew("square", 4, 5); new_square.newPerimeter();

But I was wondering, if all what you wanted to do is just calculating the perimeter, then why don't you just multiply the sides with side length?!

 class ShapeNew { constructor(name, sides, sideLength) { this.name = name; this.sides = sides; this.sideLength = sideLength; } perimeter() { return this.sideLength * this.sides; } } let new_square = new ShapeNew("square", 4, 5); console.log(new_square.perimeter());