javascript - JavaScript 中的递归出现错误

Question

var summation = function(num) {
  if (num <= 0) {
    console.log("number should be greater than 0");
  } else {
    return (num + summation(num - 1));
  }
};
console.log(summation(5));

它给了我 NaN 错误，但我想要数字的求和。我在哪里犯了错误？

Answer 1

在上一次迭代中，您正确检查输入是否为 <= 0 ，但随后不返回任何内容，这会导致隐式返回值 undefined .

添加undefined数字结果为 NaN :

console.log(1 + undefined); // NaN

要解决此问题，请返回 0如果您的取消条件已满足:

var summation = function(num) {
  if (num <= 0) {
    console.log("number should be greater than 0");
    return 0;
  } else {
    return (num + summation(num - 1));
  }
};
console.log(summation(5));