如何在JavaScript中使用indexOf()查找所有匹配项的索引

针对你给出的数组，这里提供几种实用的方法来获取所有匹配元素的索引：

方法一：利用indexOf()循环查找 #

indexOf()支持第二个参数指定起始搜索位置，我们可以通过循环不断更新起始位置，直到找不到匹配项为止：

const fruits = ["apple", "orange", "banana", "apple", "grape", "apple"];
const target = "apple";
const indices = [];
let currentIndex = fruits.indexOf(target);

while (currentIndex !== -1) {
  indices.push(currentIndex);
  // 从当前索引的下一位开始继续搜索，避免重复匹配
  currentIndex = fruits.indexOf(target, currentIndex + 1);
}

console.log(indices); // 输出 [0, 3, 5]

方法二：用forEach()遍历记录索引 #

直接遍历数组的每个元素，判断是否匹配目标值，匹配则记录对应的索引：

const fruits = ["apple", "orange", "banana", "apple", "grape", "apple"];
const target = "apple";
const indices = [];

fruits.forEach((fruit, index) => {
  if (fruit === target) {
    indices.push(index);
  }
});

console.log(indices); // 输出 [0, 3, 5]

方法三：使用reduce()累积结果 #

通过reduce()方法遍历数组，将符合条件的索引累积到结果数组中：

const fruits = ["apple", "orange", "banana", "apple", "grape", "apple"];
const target = "apple";

const indices = fruits.reduce((acc, fruit, index) => {
  if (fruit === target) {
    acc.push(index);
  }
  return acc;
}, []);

console.log(indices); // 输出 [0, 3, 5]

内容的提问来源于stack exchange，提问作者Jon