mustache.js helper functions - Add a property on your data object. Use the property name to reference the helper within your template. Inside the helper, you can reference the current object as `this`.

mustache-helper-template.html

<script>
  var people = getData(); // however you get your data ...
  
  /* structure 
  
  { 
    people : [
    
    { name : "Shiva Khomini Somar Kondar Krohm" },
    { name :   ...    }
    
    ]
  }
  
  */
  
  
  // store a function in a property, 'shortName'
  people.shortName = function(){
    return this.name.substring(0,19) + '...';    
  };
  
  /* `this` value depends on what your template is doing when you call the helper. 
      We iterate over people, So we'll call it inside that loop 
  */
</script>

// your awesome stache template
<script type="text/html" id="my-template">
  {{#people}}
    <h3>{{name}}</h3>
    <span>{{people.shortName}}</span>
  {{/people}}
</script>