Google Apps Script function to replace placeholder values in an HTML template (from a draft GMail for example)

fillInHtmlTemplate.gs

/**
 * For each placeholder - "{{[placeholder]}}", strip out any HTML and replace 
 * it with the appropriate key value. An example use of this could be using the 
 * HTML from a draft GMail as a template.
 * 
 * E.g. If the obect were:
 *
 * {PlaceHolder1: newValue}
 *
 * In the template "{{PlaceHolder1}}" would be replaced with "newValue" even
 * if there were some HTML (<...>) inside the brackets.
 *
 * https://github.com/shantanu543/bulk-mail/blob/master/bulkmail.gs
 * 
 * @param {String} template HTML or plain text
 * @param {Object} rowObject replacement values: {[placeholder]: [new value]}
 *
 * @return {String} completed template
 */
   
function fillInTemplate(template, rowObject) {

  Logger.log('template: ' + template)
  Logger.log('rowObject: ' + JSON.stringify(rowObject))

  var completed = template.replace(/{{.*?}}/g, function(nextMatch) {

    Logger.log('nextMatch: ' + nextMatch)

    // Remove any HTML inside the placeholder
    var placeholderValue = nextMatch.replace(/<.*?>/g, '')
    Logger.log('placeholderValue (HTML stripped): ' + placeholderValue)

    // Strip the placeholder identifier
    placeholderValue = placeholderValue.substring(2, placeholderValue.length - 2)
    Logger.log('placeholderValue (ids removed): ' + placeholderValue)

    var nextValue = rowObject[placeholderValue]
    Logger.log('nextValue: ' + nextValue)

    return nextValue
  })

  return completed

} // fillInTemplate()