JavaScript防止按钮重复点击的两种实现方案

<button id="btn">0</button>
<script>
btn.onclick = function add(){
  btn.innerHTML = Number(btn.innerHTML) + 1;  
  btn.onclick = null;
  clearTimeout(timer);
  var timer = setTimeout(function(){
    btn.onclick = add;
    },1000);  
}
</script>

<button id="btn">0</button>
<script>
btn.onclick = (function(){
  var last = Date.now();
  return function(){
    var now = Date.now();
    if((now - last)>1000){
      btn.innerHTML= Number(btn.innerHTML) + 1;      
    }
    last = now;
  }
})();
</script>