javascript - 为什么javascript将变量视为字符串？

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Why is using “for…in” with array iteration a bad idea?
                            
                                （27个答案）
                            
                    
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在以下代码中，为什么将我视为字符串？我必须将其乘以1才能将其转换回数字。

  getPositionInArray(value, array) {
    console.log('array = ', array);

    let i = 0; // why is i a string?
    for (i in array) {
      if (array[i].toLowerCase() === value) {
        let positionOnUI = i * 1 + 1; // why can't I use i + 1?
        return positionOnUI;
      }
    }
    return null;
  }

最佳答案

只需使用普通的for循环，就不会出现此问题：

Working Example

function getPositionInArray (value, array) {
  console.log('array = ', array);
  for (let i = 0; i < array.length; i++) {
    if (array[i].toLowerCase() === value) {
      let positionOnUI = i // why can't I use i + 1?
      return positionOnUI;
    }
  }
  return null;
}