javascript - Setting the onclick event to a custom function results in syntax error -


given following example code want set onclick event function declare in same method (no function in global scope):

<html> <head> <title>title</title> </head> <body> <img id="img" class="std" src="http://www.free-animated-pictures.com/bug_crawls_on_screen.gif"/> <script type='text/javascript'> var = document.getelementbyid("img"); var func = function(){     var = document.getelementbyid("img");     if(i.classname === "std"){         i.classname = "hid";         i.style.display = "none";     }     else if(i.classname === "hid"){         i.classname = "std";         i.style.display = "block";     } }; //func = func.tostring(); //func = func.replace("function ()", "") document.body.setattribute("onclick", func); </script> </body> </html>

if use code following error when event fired:

uncaught syntaxerror: unexpected token (

if instead take string of function , remove function part of it, script works expected:

func = func.tostring(); func = func.replace("function ()", "")

why so? there better way? can't declare function without function part, what's point in removing again?

you setting actual textual element's attribute string using setattribute, in turn auto-wrapped in function!
also, if have worked, there no body click on once image had disappeared.

here working example you should not use, intended explain above statement:

here function func converted string (and string expected, javascript calls .tostring() method automatically, put in show happened).
then, prevent quoting problem (you used double-quotes in html , (in opinion, insane) reason browsers replace single quotes in javascript double quotes (and i've witnessed pre-compiling in browsers)), naively (because safe particular function) replaced double quotes single quotes.
still need remove function(){ , trailing }.
arrived @ function string, can pass.
browser sets actual textual attribute , wraps code again inside function works.

<img id="img" class="std" src="http://www.free-animated-pictures.com/bug_crawls_on_screen.gif" />  intentional text filler, otherwise body shrinks 0*0 px leaving nothing click on...  <script type='text/javascript'>  var func = function(){       var = document.getelementbyid('img');      if(i.classname === 'std'){          i.classname = 'hid';          i.style.display = 'none';      }      else if(i.classname === 'hid'){          i.classname = 'std';          i.style.display = 'block';      }  };    document.body.setattribute( 'onclick'                            , func.tostring()                                  .replace(/\"/g,'\'')                                  .replace(/^function *\( *\) *{/,'')                                  .replace(/} *$/,'')                            );  </script>

solution document.body.onclick=func directly (as gillesc commented), or use document.body.addeventlistener('click',func,false) (which confused with).

note backward compatibility (notably < ie9) you'd need attachevent, here basic workaround:

function addeventhandler(elem, eventtype, handler) {  if (elem.addeventlistener)      elem.addeventlistener (eventtype,handler,false);  else if (elem.attachevent)      elem.attachevent ('on'+eventtype,handler);  }

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