收到错误消息：无法将属性'innerHTML'设置为null

Question

i keep getting error said: Cannot set property 'innerHTML' of null.

i try to change innerHTML ->innerText. still not working.

what am i missing here???

  function countdown(minutes) {
          var seconds = 60;
          var mins = minutes
          function tick() {
              var counter = document.getElementById("timer");
              var current_minutes = mins-1;
              seconds--;
              counter.innerHTML = 
    current_minutes.toString() + ":" + (seconds < 10 ? "0" : "") + String(seconds);
              if( seconds > 0 ) {
                setTimeout(tick, 1000);
              } else {
                if(mins > 1){
                  // countdown(mins-1);   never reach “00″ issue solved:Contributed by      
 Victor Streithorst    
                  setTimeout(function () { countdown(mins - 1); }, 1000);
              }
            }
        }
        tick();
    }        
    countdown(3);

html

   <div id="timer"></div>

Answer 1

You're calling countdown() , which calls tick() , which calls document.getElementById("timer") , before that element has even been parsed .

Try doing it like this:

<div id="timer"></div>
<script type="text/javascript">
function countdown(minutes) {
    var seconds = 60;
    var mins = minutes
    function tick() {
        var counter = document.getElementById("timer");
        var current_minutes = mins-1
        seconds--;
        counter.innerHTML = current_minutes.toString() + ":" + (seconds < 10 ? "0" : "") + String(seconds);
        if( seconds > 0 ) {
            setTimeout(tick, 1000);
        } else {

            if(mins > 1) {
                // countdown(mins-1);
                setTimeout(function () { countdown(mins - 1); }, 1000);
            }
        }
    }
    tick();
}

countdown(3);
</script>

In this case, order matters. You want to make sure the document has encountered that element before accessing it via the DOM.