html, css, javascript, jquery usage notes

//The picture is displayed centered in the div:

//javascript removes spaces at both ends
var pwd=" 123 ";
pwd=pwd.replace(/^s+|s+$/g, "" );//pwd="123"

//javascript scrolls back to the top of the interface
window.scrollTo(0,0);

//javascript regular expression to determine whether the string is composed entirely of numeric characters
if( str.match(/d/)== null)
      alert("The value entered is wrong!");
else
    alert("The value is correct!");