我的返回值显示为 NaN，我不知道为什么

Question

我正在尝试遍历数组并将所有数组值加到totalValue变量中。

const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8],

  validateCred = (arr) => {

    let totalValue;

    for (let i = arr.length - 1; i >= 0; i--) {

      let number = arr[i] * 2;

      if (number > 9) {

        totalValue += number - 9;

      }

      else {

        totalValue += number;

      }

    }

    return totalValue;

  };

console.log(validateCred(valid1));

Answer 1

给出totalValue初始值，现在它正在添加数字undefined，结果是NaNconst valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8]const validateCred = (arr) => {let totalValue = 0   for (let i = arr.length - 1; i >= 0; i--) {       let number = arr[i] *2       if (number > 9) {           totalValue += number - 9       } else {           totalValue += number       }   }   return totalValue}console.log(validateCred(valid1))你也可以使用Array.reduce这样的方法const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8]const totalValue = valid1.reduce((acc, num) => {  let number = num * 2  if (number > 9) {    acc += number - 9  } else {    acc += number  }  return acc},0)console.log(totalValue)

Answer 2

totalValue在迭代之前将 的值设置为 0 通过建立totalValue数字来解决问题。还有其他方法可以做到这一点，但我认为这是合适的。const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8]//trying to loop through the array and sum all the array values in totalValue variableconst validateCred = (arr) => {let totalValue = 0;   for (let i = arr.length - 1; i >= 0; i--) {       let number = arr[i] *2;       if (number > 9) {           totalValue += number - 9       } else {           totalValue += number       }   }   return totalValue}console.log(validateCred(valid1))

Answer 3

您的 totalValue 未初始化。const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8];const validateCred = (arr) => {    let totalValue = 0;    for (let i = arr.length - 1; i >= 0; i--) {        let number = arr[i] * 2        if (number > 9) {            totalValue += number - 9        } else {            totalValue += number        }    }    return totalValue}console.log(validateCred(valid1))