Question

What is the best way to prevent users from entering negative values in an input text element?

Currently I am checking the field value on blur, but I am hoping somebody has a better solution.

$(".payment").blur(function() {
    var payment = getAmount($(this).val());
    if(!isNaN(payment) && amount >= 0) {
        $(this)
            .css("color", "black")
            .val(currency(payment));
    } else {
        if(amount < 0) showMessage("Negative amounts are not allowed", "error");
        $(this).css("color", "red");
    }
});

function getAmount(strAmount) {
    var amount = new String(strAmount).replace(/\$/g, "").replace(/,/g, "");
    return parseFloat(amount);
}

Answer 1

You could use jQuery’s .keypress() and prevent the default action for the – key.
Example: http://jsfiddle.net/5cgXg/

$("#target").keypress(function(event) {
  if ( event.which == 45 || event.which == 189 ) {
      event.preventDefault();
   }
});