实例数组，如何知道特定实例在数组中的索引

var instances = [instance1, instance2, instance3, instance4];
var index = instances.indexOf(instance3);
console.log(index); // 输出2

var instances = [instance1, instance2, instance3, instance4];
var targetInstance = instance3;
var index = -1;

for (var i = 0; i < instances.length; i++) {
  if (instances[i] === targetInstance) {
    index = i;
    break;
  }
}

console.log(index); // 输出2

var instances = [instance1, instance2, instance3, instance4];
var targetInstance = instance3;
var index = binarySearch(instances, targetInstance);

console.log(index); // 输出2