Interview question: dynamically create N input nodes with +- in between inputs. Evaluate expression. Numbers allowed only.

gistfile1.txt

<div id="container"></div>
<div id="result"></div>
<input type="submit" id="submit-button" />

<script>

  VIKI = {
		init: function(){
			var inputs = this.createNodes(5);
			this.computeValue(inputs);
		},
		createNodes: function(numOfInputs){
			var container = document.getElementById('container'),
				inputElem, 
				selectMenuElem, 
				optionElem1, 
				optionElem2, arr = [];
			
			for(var i = 0; i<numOfInputs; i++){

				inputElem = document.createElement('input'),		
				inputElem.id = 'input' + i;

				arr.push(inputElem);
				container.appendChild(inputElem);

				if(i < (numOfInputs - 1) ){
					optionElem1 = document.createElement('option');
					optionElem1.value = 'add';
					optionElem1.innerHTML = 'add';
					
					optionElem2 = document.createElement('option');
					optionElem2.value = 'subtract';
					optionElem2.innerHTML = 'subtract';
					
					selectMenuElem = document.createElement('select');
					selectMenuElem.appendChild(optionElem1);
					selectMenuElem.appendChild(optionElem2);
					
					arr.push(selectMenuElem);
					container.appendChild(selectMenuElem);
				}
			}
			return arr;
		},
		validate: function(arr){
			for(var i = 0; i < arr.length; i++){
				if(arr[i].nodeName == 'INPUT' && isNaN(parseInt(arr[i].value)))	{ 
					return true;
				}
			}
		},
		computeValue: function(arr){
			var submitBttn = document.getElementById('submit-button'),
				resultDiv = document.getElementById('result'), 
				stringArr, 
				operator
				self = this;
			
			submitBttn.onclick = function(){
				stringArr = []; // reset
				if(self.validate(arr)) { 
					resultDiv.innerHTML = 'Must input a number in all input fields.'
					return; 
				}
				for(var i = 0; i < arr.length; i++){
					if(arr[i].nodeName === 'INPUT'){
						stringArr.push(arr[i].value);
					} else if(arr[i].nodeName === 'SELECT'){
						operator =  arr[i].options[arr[i].selectedIndex].value == 'add' ? '+' : '-';
						stringArr.push(operator);
					}
				}
				resultDiv.innerHTML = eval(stringArr.join(''));
			}
		}
	}

	VIKI.init();
	
</script>