te')); return $arr; } /* 遍历用户所有主题 * @param $uid 用户ID * @param int $page 页数 * @param int $pagesize 每页记录条数 * @param bool $desc 排序方式 TRUE降序 FALSE升序 * @param string $key 返回的数组用那一列的值作为 key * @param array $col 查询哪些列 */ function thread_tid_find_by_uid($uid, $page = 1, $pagesize = 1000, $desc = TRUE, $key = 'tid', $col = array()) { if (empty($uid)) return array(); $orderby = TRUE == $desc ? -1 : 1; $arr = thread_tid__find($cond = array('uid' => $uid), array('tid' => $orderby), $page, $pagesize, $key, $col); return $arr; } // 遍历栏目下tid 支持数组 $fid = array(1,2,3) function thread_tid_find_by_fid($fid, $page = 1, $pagesize = 1000, $desc = TRUE) { if (empty($fid)) return array(); $orderby = TRUE == $desc ? -1 : 1; $arr = thread_tid__find($cond = array('fid' => $fid), array('tid' => $orderby), $page, $pagesize, 'tid', array('tid', 'verify_date')); return $arr; } function thread_tid_delete($tid) { if (empty($tid)) return FALSE; $r = thread_tid__delete(array('tid' => $tid)); return $r; } function thread_tid_count() { $n = thread_tid__count(); return $n; } // 统计用户主题数 大数量下严谨使用非主键统计 function thread_uid_count($uid) { $n = thread_tid__count(array('uid' => $uid)); return $n; } // 统计栏目主题数 大数量下严谨使用非主键统计 function thread_fid_count($fid) { $n = thread_tid__count(array('fid' => $fid)); return $n; } ?>if statement - Javascript run once using if condition? - Stack Overflow

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    What I'm trying to do is run the if statement once only and disable the statement. In my code if I click the button consecutively the if statement still get rendered. Why is that?

    HTML:

    <button onclick="appendMsg()">submit</button>
<div id="wrapper"></div>

    Javascript:

    function appendMsg(){

  var triggerOnceforShare = true;

  if(triggerOnceforShare){
     triggerOnceforShare = false;
    document.getElementById('wrapper').innerHTML+=triggerOnceforShare + "<br />"
    console.log(triggerOnceforShare);
  }

}

    codepen:

    What I'm trying to do is run the if statement once only and disable the statement. In my code if I click the button consecutively the if statement still get rendered. Why is that?

    HTML:

    <button onclick="appendMsg()">submit</button>
<div id="wrapper"></div>

    Javascript:

    function appendMsg(){

  var triggerOnceforShare = true;

  if(triggerOnceforShare){
     triggerOnceforShare = false;
    document.getElementById('wrapper').innerHTML+=triggerOnceforShare + "<br />"
    console.log(triggerOnceforShare);
  }

}

    codepen: http://codepen.io/vincentccw/pen/uoBkI

    • javascript
    • if-statement
    • conditional-statements
    Share Improve this question asked Feb 14, 2014 at 8:43 Vincent ChuaVincent Chua 1,0096 gold badges21 silver badges41 bronze badges
    Add a ment  | 

    6 Answers 6

    Reset to default 7

    You should put your var triggerOnceforShare = true; outside the function, as global and it will works.

    var triggerOnceforShare = true;
function appendMsg(){   
  if(triggerOnceforShare){
    triggerOnceforShare = false;
    document.getElementById('wrapper').innerHTML+=triggerOnceforShare + "<br />"
    console.log(triggerOnceforShare);
  }
}

    The variable triggerOnceforShare is re-initialized every time you run your appendMsg function - so it is always set to true.

    The way to ensure it is only run once is to store the variable in a closure:

    // Using the revealing module pattern
// we create a closure using an immediately invoked function expression (IIFE)
var appendMsg = (function() {
  // We store the boolean flag in this IIFE's closure scope
  var triggerOnceforShare = true;

  // And then we return a function from our IIFE to bind to our `appendMsg` var
  return function appendMsg(){
    if(triggerOnceforShare){
      // Which changes the value of `triggerOnceForShare` in *the parent's* scope
      triggerOnceforShare = false;
      document.getElementById('wrapper').innerHTML+=triggerOnceforShare + "<br />"
    }
  }
})();

    In fact, this sort of pattern can be generalized into a function which decorates another function:

    function once(f) {
  var hasRun = false;
  return function() {
    if (hasRun) { return; }
    return f.apply(this, arguments);
  };
}

    which we could then use to simplify our code:

    var appendMsg = once(function appendMsg() {
  document.getElementById('wrapper').innerHTML+= "true<br />"
});

    Try this, Move the var triggerOnceforShare = true; from inside the function into outside

    var triggerOnceforShare = true;
function appendMsg(){   
  if(triggerOnceforShare){
     triggerOnceforShare = false;
     document.getElementById('wrapper').innerHTML+=triggerOnceforShare + "<br />"
     console.log(triggerOnceforShare);
    }
}  

    <script>
var triggerOnceforShare = true;
function appendMsg(){

  if(triggerOnceforShare){
     triggerOnceforShare = false;
    document.getElementById('wrapper').innerHTML+=triggerOnceforShare + "<br />"
    console.log(triggerOnceforShare);
  }

}
</script>

    Try this pls...

    you have to declare the variable outside the function appendMsg()

    var triggerOnceforShare = true;

function appendMsg(){        

   if(triggerOnceforShare){
       triggerOnceforShare = false;
      document.getElementById('wrapper').innerHTML+=triggerOnceforShare + "<br />"
      console.log(triggerOnceforShare);
   }    
}

    Everything in the function gets ran when the function gets called, this includes the triggerOnceforShare = true statement.

    You can either do this;

    function appendMsg() {
    if (appendMsg.ran)
        return;
    appendMsg.ran = true;

    document.getElementById('wrapper').innerHTML += triggerOnceforShare + "<br />"
}

    Which saves the ran state to the function once ran, and if it's ran again, immediately returns.

    Or you could do something more efficient. Modify your onclick to this; onclick="appendMsg(this)" and use this;

    function appendMsg(button) {
    button.onclick = null;
    document.getElementById('wrapper').innerHTML += triggerOnceforShare + "<br />"
}

    Which removes the handler from the button once ran.

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