1.return false

  1. <body>
  2.     <a href="www.baidu.com" id="a">a</a>
  3.  <script>
  4.  var a=document.querySelector("#a")
  5.  a.onclick=function(){
  6.       return false      
  7.  }
  8.  </script>
  9. </body>

2. e.preventDefault()

  1.     <body>
  2.         <a href="www.baidu.com" id="a">a</a>
  3.     <script>
  4.     var a=document.querySelector("#a")
  5.     a.onclick=function(e){
  6.         // return false  
  7.         e.preventDefault()    
  8.     }
  9.     </script>
  10.     </body>