create polynomial from array and multiply them in javascript

index.tsx
function createPolynomial(arr) {
  let poly = "";
  for (let i = arr.length - 1; i >= 0; i--) {
    if (arr[i] !== 0) { // only add non-zero terms
      let sign = arr[i] > 0 ? "+" : "-";
      let coef = Math.abs(arr[i]);
      let power = i === 0 ? "" : i === 1 ? "x" : "x^" + i;
      poly += ` ${sign} ${coef}${power}`;
    }
  }
  return poly.replace(/^\s*\+/, ""); // remove leading plus sign
}

function multiplyPolynomials(poly1, poly2) {
  let result = [];
  let degree = poly1.length + poly2.length - 2; // highest degree of result
  for (let i = 0; i <= degree; i++) {
    result[i] = 0;
    for (let j = 0; j <= i; j++) {
      result[i] += (poly1[j] || 0) * (poly2[i - j] || 0);
    }
  }
  return createPolynomial(result);
}

let poly1 = [1, 2, 3]; // 1x² + 2x + 3
let poly2 = [4, 5]; // 4x + 5
let result = multiplyPolynomials(poly1, poly2); // 4x³ + 13x² + 22x + 15
console.log(result);
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