Javascript to enter only positive or negative decimal number with 3 decimal places into a ASP.NET TextBox

I have one TextBox in my UserControl. Here I want enter only positive or negative decimal number with three decimal places. For example like below: 128.324, -23.453, 10, 0.453, -2, 2.34, -5.34 The TextBox should not allow to enter other characters. How to do this using J开发者_JS百科avaScript? I am not good enough in JavaScript.

If you validate on change your should be alright. Make sure you also validate any data that is sent to the server, on the server, since any data can be sent no matter how you try to validate it with JS:

var input = document.getElementById('tehinput');
input.onchange = function(){
    var val = this.value, sign = '';
    if(val.lastIndexOf('-', 0) === 0){
        sign = '-';
        val = val.substring(1);
    }
    var parts = val.split('.').slice(0,2);
        if(parts[0] && parseInt(parts[0], 10).toString() !== parts[0]){
        parts[0] = parseInt(parts[0], 10);
        if(!parts[0])
            parts[0] = 0;
    }
    var result = parts[0];
    if(parts.length > 1){
        result += '.';
        if(parts[1].length > 3 || 
          parseInt(parts[1], 10).toString() !== parts[1]){
              parts[1] = parseInt(parts[1].substring(0,3), 10);
              if(!parts[1])
                  parts[1] = 0;
        }
        result += parts[1];
    }
    this.value = sign+result;
}

JSFiddle

A regular expression to check content would be something like:

var re = /^[+-]?[\d,]+(\.\d{3})?$/;

but that will not enforce a comma for thousands, only allow it somewhere in the integer part. Note that in some countries, a comma is used for the decimal point.