如果值存在，为什么indexOf（char）为0？

Question

为什么firstHalf.indexOf(secondHalfArr[i]) 0？

"use strict";
let word = "9999999999",
  len = word.length,
  oddSecondHalfStarter = (len % 2 == 0) ? len / 2 : 1 + len / 2,
  firstHalf = word.substr(0, len / 2),
  secondHalf = word.substr(oddSecondHalfStarter, len),
  firstHalfArr = word.substr(0, len / 2).split(''),
  secondHalfArr = word.substr(oddSecondHalfStarter, len).split(''),
  firstHalfLength = firstHalf.length,
  secondHalfLength = secondHalf.length,
  charsToReplace = 0;

for (let i = 0; i < firstHalfLength; i++) {
  if (firstHalf.indexOf(secondHalfArr[i]) < 1) {
    charsToReplace++;
  }
}

for (let i = 0; i < secondHalfLength; i++) {
  if (secondHalf.indexOf(firstHalfArr[i]) < 1) {
    charsToReplace++;
  }
}

alert(charsToReplace);

Answer 1

indexOf()方法返回字符串中第一次出现指定值的位置。

如果要搜索的值永远不会发生，则此方法返回 -1 。 indexOf()方法区分大小写。

请务必在语句中使用!== -1以获得有效结果。

示例：

for (let i = 0; i < secondHalfLength; i++) {
  if (secondHalf.indexOf(firstHalfArr[i]) !== -1) {
    charsToReplace++;
  }
}