node-red-contrib-string

Provides a node with native and extended chainable JavaScript string parsing and manipulation methods. The node is a high level wrapper for the concise and lightweight stringjs.com object and uses Node-RED's editor UI to create easy chaining. Additional string parsing functionality and compatibility have been added from the fork.

Applies string methods from a given context property and assigns the results optionally to the same or another context property. Methods can be chained by adding multiple methods sequentially and with parameters that are literal or from other context properties. The string object always passes along the msg object with (if any) changes applied.

By default, string "from" and "to" apply to the msg.payload property but may be set to any property of global, flow, or msg contexts.

Examples

Data Extraction - Get Technical FAX

Methods can be chained within the UI enabling complex and versatile parsing functionality. Here we can see how easy it is to extract the technical FAX phone number WhoIS information:

Consider the given WhoIS dump from a command line console (see image below). We will want to obtain the FAX number (outlined in the dashed yellow). The string node will extract the technical FAX phone number by first removing the header, followed by all data up to the phrase "Technical:". This ensures that we don't accidentally obtain a FAX number from another section. Lastly, the string node grabs the number from between the markers "Fax:" and a carriage return and displays the output in the Node-RED debug window.

The extraction is performed using JavaScript's unique ability to chain actions on a given object such as the native String object or the popular jQuery component. This unique contribution to Node-RED furnishes a lightweight and enhanced version of string parsing functions. The visual representation in the first image could be coded by hand in JavaScript (after including all the dependencies) as:

console.log(
  msg.payload.getRightMost('%')
             .delLeftMost('Technical:')
             .between('FAX:', '\n')
);

Validate Phone Number

Furthermore, a single string node could have the properties set to perform data validation. In this simple example we'll perform some conditional checks to see if the phone number is numeric and furnish a friendly error message if it is not. Consider the following flow:

Let's take a look at the string node titled "Verify Number" (see image below). The properties for the node have been configured to use the methods stripPunctuation and isNumeric which will result in a boolean true or false. Next, we convert the boolean to a string using toString. Lastly, we use the replaceAll methods to convert the only two boolean possibilities to the original number as found in property msg.payload or the informative error message "Error! Not a valid number.".

Using String in Node-RED Function Nodes

You can use the string object's methods inside Node-RED's function nodes. The dependency string.js for Node.js will have already been installed if you included the string node in your palette. This would allow you to use the parsing methods in JavaScript such as:

  // Always change the last word to World
  var greet = S("Hello Mars");
  msg.payload = greet.delRightMost(" ").append("World");

There are several easy ways to make the string object's methods available in your JavaScript function nodes:

Include String Node in Flow

A simple way is to just include the string node in your flow before the Node-RED function node. The string node will normally return a native JavaScript string datatype; however, if you use the setValue method with no value, a string.js object can be casted into a readily available property. In our example below we cast the object into msg.string.

The string object returns an instance of itself when using the setValue method. You can then write JavaScript to instantiate a copy of the string object.

var S = function(x) {
  return msg.string.setValue(x);
}
msg.payload = S("Hello World");

Enable Require in Node-RED

An alternative method to use the string object is to enable the require method by updating Node-RED's settings.js to enable Node.js' "require" ability.

node-red/node-red#41 (comment)

functionGlobalContext: {
    require:require,
    // os:require('os'),
    // octalbonescript:require('octalbonescript'),
    // jfive:require("johnny-five"),
    // j5board:require("johnny-five").Board({repl:false})
},

This will essentially give Node-RED's function node the ability to include any arbitrary Node.js library which you may or may not desire. Likewise, you could just update Node-RED's settings.js to just enable the string.js library by modifying the functionGlobalContext to read:

functionGlobalContext: {
    string:require("string")
},

Your Node-RED's function node could then instantiate a string object like so:

var S = global.get("string");
msg.payload = S("Hello World");

Installation

Run the following command in your Node-RED user directory (typically ~/.node-red):

npm install node-red-contrib-string

The string node will appear in the palette under the function group.

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