setInterval · JavaScript

## setinterval 隔一段事件执行,并且会重复执行. ``` <body> <input type="button" id="btn1" value="开始"> <input type="button" id="btn2" value="取消"> <script> var btn1 = document.getElementById('btn1'); var timerId; //定时器的标识 btn1.onclick = function () { var num = 1; //第一次执行也要等3秒钟 timerId = setInterval(function () { console.log('定时任务' + (num++)); }, 3000) } var btn2 = document.getElementById('btn2'); btn2.onclick = function () { clearInterval(timerId); } </script> ``` ## 倒计时案例 ``` ```