Improving JavaScript performance with local variables skillfully

  Use local variables to effectively improve JavaScript performance, here is a good example, you can refer to the following

The deeper the location of an identifier in JavaScript, the slower the read and write speed. Therefore, reading and writing local variables is always the fastest in a function, while reading and writing global variables is usually the slowest. A good rule of thumb is that if a value across a scope is referenced more than once in a function, it is stored in a local variable.     Example:    code as follows: <!--optimization-->  <script type= "Text/javascript" >  function Initui () {  var bd = document.body,  links = document.getelementbytagname ("a"),  i=0,  len=links.length;& nbsp while (I < len) {  update (links[i++]); }    document.getElementById ("go-btn"). onclick = function () {  start (); }    Bd.classname = "active"; }  </script>    The function refers to the document three times, and document is a global object. The process of searching for this variable must traverse the entire scope link until it is finally found in the global variable object. You can reduce the impact on performance by first storing a reference to a global variable in a local variable and then using that local variable instead of a global variable.     Example:    code as follows: <!--optimized-->  <script type= "Text/javascript" >  function Initui () {  var doc=document,  bd = doc.body,  links = doc.getelementbytagname ("a"),  i=0, . length;  while (i < len) {  update (links[i++]); }    Doc.getelementbyid ("go-btn"). onclick = function () {  start (); }    Bd.classname = "Active"; }  </script>