数组索引背后隐藏了哪些类型转换？

let a = new Array();
a[0] = 1;
a["0"] = 2;
a[0]++;
console.log('a["0"]的输出是', a["0"]);
console.log('a[0]的输出是', a[0]);
//a["0"]的输出是 3
//a[0]的输出是 3

let arr = [];
arr[5] = "Hello";
console.log(arr["5"]);
// Hello

let obj = [];
let key = {a:1};
obj[key] = "value";
console.log(obj["[object Object]"])
// value

let arr = [];
function myFunction() {
  return "promptonce";
}
arr[myFunction] = "函数作为索引";
console.log(arr[myFunction]);
// 函数作为索引

let arr = [];
let symIndex = Symbol("index");
arr[symIndex] = "Hello";
console.log(arr[symIndex]);
// Hello

let arr = [];
let symIndex = Symbol("index");
arr[symIndex] = "Hello";

let string = symIndex.toString();
console.log(string)
console.log(arr[string]);
// Symbol(index)
// undefined