倒计时

let second = 5,
let timePromise = undefined;
let _this = this;
timePromise = setInterval(function() {
    if (second <= 0) {
        clearInterval(timePromise);
        second = 5;
         _this.setState({
            codeText: '获取验证码',
          });
    } else {
         _this.setState({
            codeText: '重新获取(' + second + ')',
         }, () => {
             second--;
         });
       }
}, 1000);