Node-RED - Voorbeeld - Save variable to disk

On this page we give an example and some back=information how to store a node-red variable to disc, so that after a shutdown it can retrieve the data back again.

Some guides here:
https://nodered.org/docs/user-guide/context
https://stevesnoderedguide.com/node-red-variables

Example 1 – In a function

To enable disc writing, edit the node-red settings.js file (mostly found in home/pi/.node-red)

Add these lines (they can also be found in the text)

contextStorage: {
   default: "memoryOnly",
   memoryOnly: { module: 'memory' },
   file: { module: 'localfilesystem' }
},

contextStorage: {

default: "memoryOnly",

memoryOnly: { module: 'memory' },

file: { module: 'localfilesystem' }

Then when you want to store a value from a function you can use for example:

var count = 25;
context.set("count", count, "file");

return msg;

var count = 25;

context.set("count", count, "file");

return msg;

The value will be written every 30 seconds.

Where is it stored?

Official docs: https://nodered.org/docs/api/context/store/localfilesystem#options

There is a JSON file created with the value in de .node-red/context folder, for example:

.node-red/context/ae043a50.ff6048/44f81811.9a5e08.json

Where the foldername is the Flow ID (ae043a50.ff6048)

And the filename is the Node Id (44f81811.9a5e08)

Contents of the JSON file (with the example above)

{
    "count": 25
}

{

"count": 25

}

To retrieve the value, use in a fucntion:

msg.payload = context.get("count", "file");

return msg;

msg.payload = context.get("count", "file");

return msg;

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Node-RED – Voorbeeld – Save variable to disk

Example 1 – In a function

Where is it stored?