How to dynamically change the contents of a function using JavaScript -

to understand function in html page , generated, cannot change generated code:

function update_qu7260() {   var newval = ''   for( var idx = 0; idx < 2; idx++ )   {     var test     if( idx == 0 ) test = text7263     else if( idx == 1 ) test = text7265     if( test.matchobj ) newval += test.leftsel + "-" + test.matchobj.rightsel + ","   }   newval = newval.substring( 0, newval.length-1 )   varquestion_0001.set( newval )   qu7260.hasbeenprocessed=false;   doimmfeedback('qu7260'); } var qu7260 = new object(); ... qu7260.updfunc = update_qu7260; var qobj=[qu7260]; 

note in above number "7260", numbers start @ 1 there lots of them , each update_###() different cannot re-write them "hard wired" code. code in external javascript file , executed onload:

... var updfunc = qobj[0].updfunc.tostring(); if(updfunc.indexof('doimmfeedback(')!=-1){   updfunc = updfunc.replace('doimmfeedback','doimmquestionfeedback');  // function   updfunc = updfunc.replace('function ','');  // remove word function   var funcname = updfunc.substr(0,updfunc.indexof('('));  // function name e.g. update_qu7260   updfunc = "window['" + funcname + "']=function" + updfunc.replace(funcname,'');   eval(updfunc); } ... 

when change eval() alert() can see it's correct, however, eval() not raising errors , function doimmquestionfeedback not being called. when subsequently alert(qobj[0].updfunc.tostring()) see original function.

it seem have provided information complex, following code better example:

function hi(){alert('hi');} function changehi(){    hi(); // alert box hi    newhi = "function hi(){alert('hi there');}"    eval(newhi);    hi(); // alert box hi    window.settimeout('hi()',500); // alert box hi } window.settimeout('changehi()',500); 

the following original question:

i have predefined function did not create, however, know it's name can function , change doing:

var functext = window.updatefunc.tostring(); functext = functext.replace('dosomeotherfunction(','domyfunction('); 

how update actual function did before except call domyfuntion()?

the following example visualize want do, actual function need change complex. have:

function updatefunc(whattoupdate,true){    ... - lots of stuff.    var retval = dosomeotherfunction(whattoudate);    ... - lots of stuff based on retval } 

i need change to:

function updatefunc(whattoupdate,true){    ... - lots of stuff    var retval = domyfunction(whattoudate);    ... - lots of stuff based on retval, have had chance change retval } 

then first thing function call dosomeotherfunction() check/change returned value , subsequently return value updatefunc().

i have tried manipulate functext above to:

functext = 'window.updatefunc = function(...'; eval(functext); 

without success.

this may closed enough looking for.

assuming have original function:

function originalfunc(val) {     // function converts input string upper case     return val.touppercase(); } 

now want override either before or after execute function (in example, execute before, of course before or after doesn't matter in case).

// preserve orignal function var originalfunc_save = originalfunc;  // override original function block     var originalfunc = function(text) {     // lets call orignal function     text = originalfunc_save(text);      // our custom thing     return text.split('').reverse().join(''); } 

so our test should work.

var text = 'this test'; console.log(originalfunc(text)); 

output:

tset si siht 

this method works if have override functions inside class. thing have careful of choose saved name doesn't interfere original class code. _save may not enough, idea.

update: i'm updating code above use string variable pointing original function. think op wanted.

original code defined library

function originalfunc(val) {     // function converts input string upper case     return val.touppercase(); } 

now use func string variable point function , execute it.

var text = 'this test'; var func = 'originalfunc'; text = window[func](text); console.log(text); 

output: of course original intended result because haven't overridden it.

this test 

now write our code override original function behavior using string pointing function.

// let's define new function string var funcsaved = func + '___saved';  // preserve original function code window[funcsaved] = window[func];  // override original function code block window[func] = function(text) {     // lets call orignal function     text = window[funcsaved](text);      // our custom thing     return text.split('').reverse().join(''); }  // let's test code text = 'this test'; text = window[func](text); console.log(text); 

output:

tset si siht