validatePhone.js

_isNumber = (n) => {
    return !isNaN(parseFloat(n)) && isFinite(n);
  }
adaptPhone = (val) => {

  const deleteLastChar = (val) =>{
      val = val.substring(0, val.length - 1);
      if(val[0] != '+'){
          val = '+7'+val;
      }
      return val;
  }

  if (val[0]!='+' && val.length == 1){
      val = '+7'
  }

  if(!this._isNumber(val)||val.length>12){
    return deleteLastChar(val)
  }

  return val
}