Uncaught TypeError: window.showModalDialog is not a function

if(window.showModalDialog == undefined){ window.showModalDialog = function(url,mixedVar,features){ 
window.hasOpenWindow = true; 
if(mixedVar) var mixedVar = mixedVar; 
if(features) var features = features.replace(/(dialog)|(px)/ig,"").replace(/;/g,‘,‘).replace(/\:/g,"="); 
window.myNewWindow = window.open(url,"_blank",features); 
} }