如何获取数组中元素的索引？

function getIndex(arr, target) {
  for (var i = 0; i < arr.length; i++) {
    if (arr[i] === target) {
      return i;
    }
  }
  return -1; // 如果未找到目标元素，返回-1
}

var array = [1, 2, 3, 4, 5];
var targetElement = 3;
var index = getIndex(array, targetElement);
console.log(index); // 输出：2

var array = [1, 2, 3, 4, 5];
var targetElement = 3;
var index = array.indexOf(targetElement);
console.log(index); // 输出：2

var array = [1, 2, 3, 4, 5];
var targetElement = 3;
var index = array.findIndex(function(element) {
  return element === targetElement;
});
console.log(index); // 输出：2