title: How to validate checkbox values using express-validator?
body: <p>In my web front end form, I am using checkbox to select list of companies for each checkbox entry, I have given company name as 'value' attribute. In nodejs, I use express-validator to check the form. I am not clear how to validate and sanitize user input for these checkbox items.</p>
  
  <p>I see all the example of express validator uses form parameter name to check a specific parameter (eg) check('userName') as middleware. But for checkboxes particular parameter will be present only when the user select that parameter. If I have 10 options and user select only 4 of them, then req.body will have only these parameters . And also I want all them pass through same validation check and sanitization. Please suggest how to do it.</p>
  
  <p>I am using NodeJS version: 10.8
  Express Validator: 5.3.0
  My checkbox values are company_a1,company_a2,...company_a10. I tried to write custom Validator and check for each of the body parameter for alphanumeric value, but check is not raising error even if the value contain alphanumeric strings</p>
  
  <pre><code>async function validateReportParams(body, { req, loc, rpath }) {
  
   for (const par of Object.keys(req.body)) {
      try {
        check(req.body[par].isAlphanumberic());
      } catch (err) {
          return Promise.reject(err);
      }
    }
  }
  exports.genReport = [
    validateReq,
    param().custom(validateReportParams),
    async (req, res, next) =&gt; { ... }
  ];
  
  </code></pre>