Strange work RegExp in javascript

Question

I want validate user input. User may input four digit only. I use RegExp for checking and see strange work. Javascript not understand \d

var expr1 = new RegExp("^\s*[0-9]{4,4}\s*");
var year = "1984";
alert (expr1.test(year));


var expr2 = new RegExp("^\s*\d{4,4}\s*");
alert (expr2.test(year));

It alerting "true" and "false". http://jsfiddle.net/HfHDu/

Why?

Answer 1

Always escape \ when using RegExp constructor

var expr1 = new RegExp("^\\s*[0-9]{4,4}\\s*");
var year = "1984";
alert (expr1.test(year)); //true


var expr2 = new RegExp("^\\s*\\d{4,4}\\s*");
alert (expr2.test(year)); //true

Answer 2

Try using using \\d in place of \d.