JavaScript 迭代器协议

var a = {}; a[Symbol.iterator]=function(){var i=0;return {next:()=>{return {value:i++,done:i>20};}}} [...a]  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]