title: make an input only-numeric type on knockout
body: <p>i read many tutorials but i dont know how to do this, this is the input</p>
  
  <pre><code>input(type="text",name="price",id="price"data-bind="text: price,valueUpdate:['afterkeydown','propertychange','input']")
  </code></pre>
  
  <p>and this is my viewModel</p>
  
  <pre><code>price: ko.computed(function()
  {
      return parseFloat(this.replace(' ','').replace(/[^0-9\.]+/g,"")) || '';
  },this)
  </code></pre>
  
  <p>but this cause error: this has no method replace??? how can i pass the price value to the computed function??</p>