basic-shape-areas.js

const calculateRectangleArea = function (length, width) {
  if(length <= 0 || width <= 0) {
    return;
  } else {
    return length * width;
  }
}

const calculateTriangleArea = function (base, height) {
  if(base <= 0 || height <= 0) {
    return;
  } else {
    return base * height / 2;
  }
  
}

const calculateCircleArea = function (radius) {
  if (radius <= 0) {
    return;
  } else {
    return Math.PI * radius ** 2;
  }
}

console.log(calculateRectangleArea(10, 5));     // should print 50
console.log(calculateRectangleArea(1.5, 2.5));  // should print 3.75
console.log(calculateRectangleArea(10, -5));    // should print undefined

console.log(calculateTriangleArea(10, 5)); // should print 25
console.log(calculateTriangleArea(3, 2.5)); // should print 3.75
console.log(calculateTriangleArea(10, -5)); // should print undefined

console.log(calculateCircleArea(10)); // should print 314.159...
console.log(calculateCircleArea(3.5)); // should print 38.484...
console.log(calculateCircleArea(-1)); // should print undefined