I think you want to test your RegExp in TypeScript, so you have to do like this:
var trigger = "2",
regexp = new RegExp('^[1-9]\d{0,2}$'),
test = regexp.test(trigger);
alert(test + ""); // will display true
You should read MDN Reference - RegExp, the RegExp object accepts two parameters pattern and flags which is nullable(can be omitted/undefined). To test your regex you have to use the .test() method, not passing the string you want to test inside the declaration of your RegExp!
Why test + ""?
Because alert() in TS accepts a string as argument, it is better to write it this way. You can try the full code here.