Question

对于以下javascript代码

function hasSpecialColumn(arr) {
  for (let col = 0; col < arr[0].length; col++) {

      let sumOfOnes = 0;

      for (let row = 0; row < arr.length; arr++) {
          if (arr[row][col] === 1) {
              sumOfOnes++;
              if (sumOfOnes >= 2) {
                  return true;
              }
          }
      }

  }
  return false;
}

const arr = [[3,4],[5,6]];
console.log(hasSpecialColumn(arr));

Nodejs出现以下错误。

 Users/khaymahd/workspace/iv/for-loop-undefined-error.js:3
      for (let col = 0; col < arr[0].length; col++) {
                                    ^

    TypeError: Cannot read property 'length' of undefined
    at hasSpecialColumn (/Users/khaymahd/workspace/iv/for-loop-undefined-error.js:3:37)
    at Object.<anonymous> (/Users/khaymahd/workspace/iv/for-loop-undefined-error.js:21:17)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.runMain (module.js:604:10)
    at run (bootstrap_node.js:394:7)
    at startup (bootstrap_node.js:149:9)

也在chrome控制台中尝试过

VM183:3 Uncaught TypeError: Cannot read property 'length' of undefined
    at hasSpecialColumn (<anonymous>:3:38)
    at <anonymous>:21:17

这是一个奇怪的错误！但是，如果我设置size = arr [0] .length并在for循环中使用它，它将起作用。但是我不明白为什么原始代码不起作用。

Answer 1

由于似乎认为arr [0]未定义，请尝试放入console.log(arr);和console.log(arr[0])。其中之一可能会返回undefined，这会导致您当前的错误。

无法读取二维数组上for循环中未定义的属性“长度”

1 个答案: