javascript white concise calculator_javascript skills

<div id="calcuator"> 
  <input type="text" id="input-box" value="0" size="21" maxlength="21" readonly="readonly" /> 
  <div id="btn-list"> 
    <div onclick="operator('clear')" class=" btn-30 btn-radius color-red clear-marginleft"> 
      C</div> 
    <div onclick="operator('opposite')" class=" btn-30 btn-radius color-blue"> 
      +/-</div> 
    <div onclick="operator('percent')" class=" btn-30 btn-radius color-blue"> 
      %</div> 
    <div onclick="operator('backspace')" class=" btn-70 btn-radius color-red font-14"> 
      ←</div> 
    <div onclick="typetoinput('7')" class=" btn-30 btn-radius clear-marginleft"> 
      7</div> 
    <div onclick="typetoinput('8')" class=" btn-30 btn-radius"> 
      8</div> 
    <div onclick="typetoinput('9')" class=" btn-30 btn-radius"> 
      9</div> 
    <div onclick="operator('plus')" class=" btn-30 btn-radius color-blue font-14"> 
      +</div> 
    <div onclick="operator('minus')" class=" btn-30 btn-radius color-blue font-14"> 
      -</div> 
    <div onclick="typetoinput('4')" class=" btn-30 btn-radius clear-marginleft"> 
      4</div> 
    <div onclick="typetoinput('5')" class=" btn-30 btn-radius"> 
      5</div> 
    <div onclick="typetoinput('6')" class=" btn-30 btn-radius"> 
      6</div> 
    <div onclick="operator('multiply')" class=" btn-30 btn-radius color-blue font-14"> 
      ×</div> 
    <div onclick="operator('divide')" class=" btn-30 btn-radius color-blue font-12"> 
      ÷</div> 
    <div onclick="typetoinput('1')" class=" btn-30 btn-radius clear-marginleft"> 
      1</div> 
    <div onclick="typetoinput('2')" class=" btn-30 btn-radius"> 
      2</div> 
    <div onclick="typetoinput('3')" class=" btn-30 btn-radius"> 
      3</div> 
    <div onclick="operator('pow')" class=" btn-30 btn-radius color-blue font-14"> 
      ×&sup2;</div> 
    <div onclick="operator('sqrt')" class=" btn-30 btn-radius color-blue font-12"> 
      √</div> 
    <div onclick="typetoinput('0')" class=" btn-70 btn-radius clear-marginleft"> 
      0</div> 
    <div onclick="typetoinput('.')" class=" btn-30 btn-radius"> 
      .</div> 
    <div onclick="operator('result')" class=" btn-70 btn-radius color-red font-14"> 
      =</div> 
  </div> 
</div>

function operator(type) { 
  switch (type) { 
  case "clear": 
    input.value = "0"; 
    _string.length = 0; 
    /*document.getElementById("ccc").innerHTML=""; 
        for(i=0;i<_string.length;i++) 
        { 
          document.getElementById("ccc").innerHTML+=_string[i]+" "     
        }*/ 
    break; 
  case "backspace": 
    if (checknum(input.value) != 0) { 
      input.value = input.value.replace(/.$/, ''); 
      if (input.value == "") { 
        input.value = "0"; 
      } 
    } 
    break; 
  case "opposite": 
    if (checknum(input.value) != 0) { 
      input.value = -input.value; 
    } 
    break; 
  case "percent": 
    if (checknum(input.value) != 0) { 
      input.value = input.value / 100; 
    } 
    break; 
  case "pow": 
    if (checknum(input.value) != 0) { 
      input.value = Math.pow(input.value, 2); 
    } 
    break; 
  case "sqrt": 
    if (checknum(input.value) != 0) { 
      input.value = Math.sqrt(input.value); 
    } 
    break; 
  case "plus": 
    if (checknum(input.value) != 0) { 
      _string.push(input.value); 
      _type = "plus"input.value = "+"; 
      input.name = "type"; 
    } 
    break; 
  case "minus": 
    if (checknum(input.value) != 0) { 
      _string.push(input.value); 
      _type = "minus"input.value = "-"; 
      input.name = "type"; 
    } 
    break; 
  case "multiply": 
    if (checknum(input.value) != 0) { 
      _string.push(input.value); 
      _type = "multiply"input.value = "×"; 
      input.name = "type"; 
    } 
    break; 
  case "divide": 
    if (checknum(input.value) != 0) { 
      _string.push(input.value); 
      _type = "divide"input.value = "÷"; 
      input.name = "type"; 
    } 
    break; 
  case "result": 
    if (checknum(input.value) != 0) { 
      _string.push(input.value); 
      if (parseInt(_string.length) % 2 != 0) { 
        _string.push(_string[_string.length - 2]) 
      } 
      if (_type == "plus") { 
        input.value = parseFloat(result(_string)[0]) + parseFloat(result(_string)[1]); 
        input.name = "type" 
      } else if (_type == "minus") { 
        input.value = parseFloat(result(_string)[0]) - parseFloat(result(_string)[1]); 
        input.name = "type" 
      } else if (_type == "multiply") { 
        input.value = parseFloat(result(_string)[0]) * parseFloat(result(_string)[1]); 
        input.name = "type" 
      } else if (_type == "divide") { 
        input.value = parseFloat(result(_string)[0]) / parseFloat(result(_string)[1]); 
        input.name = "type" 
      } 
      break; 
    } 
 
  } 
}