How to detect up and down clicks on html input[number]?

Question

I have an html <input type="number"> box that has some custom validation logic. A valid value is any integer x where x < -100 OR x >= 100.

My goal is to implement this behavior:

1. when the user clicks on the native down arrow or presses the down arrow key and the current value is 100, the value changes to -101.
2. similarly when the user clicks on the native up arrow or presses the up arrow key and the current value is -101, the value changes to 100.

A few caveats:

• Users must still be able to type numbers that fall within the invalid range since they may need to type 10 in order to type 109. And validation logic already occurs for this.
• I am using angularjs, but I suspect that the solution is not going to be angular specific.
• This is an internal application, meant for Chrome only, so browser specific answers are fine.

Answer 1

I think I have what you need, or at least I'm getting close:

window.onload = function() {
  function changeNum(input, typing) {
    var lower=-101, upper=100, x=parseInt(input.value), active=(input==document.activeElement);
    if ((typing && String(Math.abs(x)).length>2 && lower<x&&x<upper) || (!typing && lower<x&&x<upper)) {
      if (Math.abs(x-upper) < Math.abs(x-lower)) {input.value = (!active||typing?upper:lower);}
      else {input.value = (!active||typing?lower:upper);}
    }
  }
  document.getElementById("num").addEventListener("keyup",function(){changeNum(this,true);},false);
  document.getElementById("num").addEventListener("change",function(){changeNum(this,false);},false);
};

<input type="number" id="num" value="100" />

jsfiddle: https://jsfiddle.net/9zz0ra35/4/
codepen: http://codepen.io/anon/pen/Ndqbog

• When the user clicks on the input's up&down-buttons, the value flips over on the lower and upper threshold (-100 -> 100, 99 -> -101).
• When the user types a value and then clicks outside the input, invalid values are changed to the closest threshold (-100 -> -101, 99 -> 100).
• While typing, invalid values are also changed to the closest threshold, but only if the value.length is more than 2 chars (-100 -> -101).
  • This last one isn't as clean as the others, because it only works if both the lower and upper threshold have the same length (in this case 3 chars).
    But if you need thresholds with different lengths, you can always change the String(Math.abs(x)).length>2 to an extra if-clause and first check whether the value is positive or negative, and then check for separate lengths.

Answer 2

I'm not sure if I'm getting what you want. Is it something like this?

 var number = document.getElementById('number-input');
 number.onchange = function(event) {
  if(number.value > 100) {
   number.value = -101;
  } else if(number.value < -100) {
   number.value = 101;
  }
 };

<input type="number" id="number-input">