var obj = { val: '', valueOf: function() { if (!this.val) { this.val = 'a' return 'a' } else if (this.val === 'a') { this.val = 'b' return 'b' } else if (this.val === 'b') { this.val = '' return 'c' } }}
var obj = { val: '', valueOf: function() { if (!this.val) { this.val = 'a' return 'a' } else if (this.val === 'a') { this.val = 'b' return 'b' } else if (this.val === 'b') { this.val = '' return 'c' } }}名师互学网 版权所有 (c)2021-2022 ICP备案号：晋ICP备2021003244-6号
