node-red/packages/node_modules/@node-red/nodes/locales/en-US/function/10-function.html

<!--
  Copyright JS Foundation and other contributors, http://js.foundation

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
-->

<script type="text/html" data-help-name="function">
    <p>A JavaScript function block written in <b>Function</b> tab to run against the messages being received by the node.</p>
    <p>The messages are passed in as a JavaScript object called <code>msg</code>.</p>
    <p>By convention it will have a <code>msg.payload</code> property containing
       the body of the message.</p>
    <p>The function is expected to return a message object (or multiple message objects), but can choose
       to return nothing in order to halt a flow.</p>
    <p>Setup code executed before deploy can be specified in <b>Setup</b> tab.  Also, cleanup code executed before flow shutdown can be specified in <b>Cleanup</b> tab.</p>
    <h3>Details</h3>
    <p>See the <a target="_blank" href="http://nodered.org/docs/writing-functions.html">online documentation</a>
    for more information on writing functions.</p>
    <h4>Sending messages</h4>
    <p>The function can either return the messages it wants to pass on to the next nodes
    in the flow, or can call <code>node.send(messages)</code>.</p>
    <p>It can return/send:</p>
    <ul>
      <li>a single message object - passed to nodes connected to the first output</li>
      <li>an array of message objects - passed to nodes connected to the corresponding outputs</li>
    </ul>
    <p>If any element of the array is itself an array of messages, multiple
          messages are sent to the corresponding output.</p>
    <p>If null is returned, either by itself or as an element of the array, no
          message is passed on.</p>
    <h4>Logging and Error Handling</h4>
    <p>To log any information, or report an error, the following functions are available:</p>
      <ul>
          <li><code>node.log("Log message")</code></li>
          <li><code>node.warn("Warning")</code></li>
          <li><code>node.error("Error")</code></li>
      </ul>
    </p>
    <p>The Catch node can also be used to handle errors. To invoke a Catch node,
    pass <code>msg</code> as a second argument to <code>node.error</code>:</p>
    <pre>node.error("Error",msg);</pre>
    <h4>Accessing Node Information</h4>
    <p>In the function block, id and name of the node can be referenced using the following properties:</p>
    <ul>
        <li><code>node.id</code> - id of the node</li>
        <li><code>node.name</code> - name of the node</li>
    </ul>
    <h4>Using environment variables</h4>
    <p>Environment variables can be accessed using <code>env.get("MY_ENV_VAR")</code>.</p>
</script>