写一个click事件处理器，防止像下面这样的默认事件，

$('a#id-of-it').on('click', function(event) {
  // Do whatever you want
  event.preventDefault();
})

html看起来像

<a href="#" id="id-of-it">Download</a>

从标签中删除下载属性

<a href="javascript:void(0);" class="classname">download</a>

或者你可以使用jquery

$('tag.classname').on('click', function(e) {
  e.preventDefault();
  //this stop default prevent or action
  or you can use 
  e.stopPropagation();
})

$('a.demo').click(function(e) {
      e.preventDefault();
      //this stop default prevent or action
      //or you can use 
      e.stopPropagation();
 })

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<a href="javascript:void(0);" class="demo" download>download</a>

或者使用javascript

document.getElementById("demo").addEventListener("click", function(e){
    e.preventDefault()
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<a href="javascript:void(0);" id="demo" download>download</a>

是的，我已经解决了<?php condition的问题
如果变量没有值，则创建不带download选项<a>标记，如果变量有值，则创建带下载的<a>标记

$('a.demo').click(function(e) {
      e.preventDefault();
      //this stop default prevent or action
      //or you can use 
      e.stopPropagation();
 })

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<a href="javascript:void(0);" class="demo" download>download</a>