title: Javascript Regex to Validate only "sentence separated by comma"
body: <p>I need to validate this string in javascript.</p>
  
  <p>the availability on the second argument is restricted to R1, R2, R3, R4
  the second and third argument can only be separated by comma, while the first and the second is by space.</p>
  
  <pre><code>req R1,1 //valid
  req R2,3 //valid
  req R0,1 //invalid
  req R1 1 //invalid
  </code></pre>
  
  <p>I have written this:</p>
  
  <pre><code>/^req\sR1|R2|R3|R4[^,][0-9]+$/
  </code></pre>
  
  <p>but it fails on few cases:</p>
  
  <pre><code>req R3 1 //supposed to be invalid, valid using above regex
  req R3.1 //supposed to be invalid, valid using above regex
  </code></pre>