Javascript:3 个函数，用于计算三角形、圆形或矩形的面积，返回未定义

Question

很抱歉这个非常简单的问题，但我似乎无法缩小为什么以下函数对所有结果都返回"未定义"。这是我的代码：

function calculateTriangleArea(x, y){
x * y / 2 
}
function calculateRectangleArea(x, y){
x * y
}
function calculateCircleArea(x){
Math.PI * x * x
}
if (calculateRectangleArea.name === true)
(function calculateRectangleArea(x, y)
{return [x * y]
})
if (calculateTriangleArea.name === true)
(function calculateTriangleArea(x, y){
return[x * y / 2]
})
else (function calculateCircleArea(x){
return [Math.PI * x * x]
})

当我运行这 9 个控制台时.log命令都返回未定义。

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

Answer 1

你缺少calculateTriangleArea、calculateRectangleArea和calculateCircleAreareturn。由于它们由其他函数在内部使用，因此您还需要从这些函数返回值：

function calculateTriangleArea(x, y) {
return x * y / 2
}
function calculateRectangleArea(x, y) {
return x * y
}
function calculateCircleArea(x) {
return Math.PI * x * x
}
if (calculateRectangleArea.name === true)
(function calculateRectangleArea(x, y) {
return [x * y]
})
if (calculateTriangleArea.name === true)
(function calculateTriangleArea(x, y) {
return [x * y / 2]
})
else(function calculateCircleArea(x) {
return [Math.PI * x * x]
})
console.log(calculateRectangleArea(10, 5));
console.log(calculateRectangleArea(1.5, 2.5));
console.log(calculateRectangleArea(10, -5));
console.log(calculateTriangleArea(10, 5));
console.log(calculateTriangleArea(3, 2.5));
console.log(calculateTriangleArea(10, -5));
console.log(calculateCircleArea(10));
console.log(calculateCircleArea(3.5));
console.log(calculateCircleArea(-1));

Answer 2

您需要返回值，您可以使用 ES6 语法。

const calculateTriangleArea = (x, y) => x * y / 2 ;