html input type number prevent insert invalid number-CodePudding

i have the following input number:

 <input type="number" id="quantity" name="quantity"  (change)="firstRangePointChanged($event)" >

I want to prevent from the user to insert invalid input like --99 (--) instead of (-) I have tried to use

if (Number.isNaN(num)) {
          event.preventDefault();

but it is not working... I want to allow a negative numbers but not --99 I want that if the user insert invalid number then return the value to the previous one (the last valid value of that input)

 firstRangePointChanged(event) {
   
    const num = parseFloat(event.target.value);
    if (Number.isNaN(num)) {
      event.preventDefault();
      return;
    }
}

CodePudding user response：

function is_validNumber(n){
  // check value is number or not
  if( n == NaN ){ return false; }
  let b = typeof n;
  if( b == 'number' || b == 'string' ){
    // Math.round(Number(n) :to supported decimal number
    return String(n).length ? Number.isInteger( Number(n) ) : false;
  }
  return false;
}
// =========================================================
function numValidation_(n){
  // add history valid number of this input
  if( n.history_validNumber == undefined ){
    n.history_validNumber = 0; // default value
  }
  
  let val_ = n.value;
  if( is_validNumber(val_) ){
    n.history_validNumber = val_; // add history
    console.log('valid');
  }else{
    // invalid
    n.value = n.history_validNumber;
    console.log(`invalid, set last valid:${n.history_validNumber}`);
  }
}

<input type="number" onchange="numValidation_(this)" />

CodePudding user response：

you can simply use regex in pattern to do that. for example:

<input type="text" id="country_code" name="country_code"
  pattern="[A-Za-z]{3}" title="Three letter country code">

remember for use pattern, you must use type:"text" to allow you to use regex in pattern