sum.html

<script type="text/x-red" data-template-name="sum">
    <div class="form-row">
        <label for="node-input-name"><i class="fa fa-tag"></i> Name</label>
        <input type="text" id="node-input-name" placeholder="Name">
    </div>
    <div class="form-row">
        <label for="node-input-topic"><i class="fa fa-tasks"></i> Topic</label>
        <input type="text" id="node-input-topic" placeholder="Topic">
    </div>
</script>

<script type="text/x-red" data-help-name="average">
    <p>Calculate the sum of incoming <code>msg.payload</code> values from across a number of different <code>msg.topic</code>.</p>
    <p>Incoming <code>msg.topic</code> has to be used to separate and identify values.
    Messages not containing a valid numeric value will be rejected.</p>
    <p>Will return the current sum of all different <code>msg.topic</code> values as <code>msg.payload</code>.
    Every other properties of incoming message will be pushed through.</p>
    <p>The sum can be reset with an incoming message that contains <code>msg.reset</code>.
    Then all stored data will be removed and the initial sum starts at zero again.</p>
</script>

<script type="text/javascript">
    RED.nodes.registerType("sum", {
      category: "function",
      defaults: {
        name: {value:""},
        topic: {value:""}
      },
      color:"#e2d96e",
      inputs: 1,
      outputs: 1,
      icon: "font-awesome/fa-plus-square-o",
      label: function() {
        return this.name || "sum";
      },
      labelStyle: function() {
        return this.name ? "node_label_italic" : "";
      }
    });
</script>