using with alert("this is alert"); this display a box with string in centre but also found ABOUT BLANK why this,

Question

why its written about/blank in alert box, can I replace that with my choice

Answer 1

No, you can't... this is a pop-up windows handle by the browser, so its title may vary, but in your configuration, if you found 'about:blank', you are probably executing javascript without html wrapper, so you are in a empty page ( about:blank ), and the title of the pop-up is the url of the page ( 'about:blank' is a special url ^^ )...