filter which drops 'seenbefore' items

You can (re)use this filter (the 'filter new items'-machine) to prevent duplicate dataflows. It installs a (userlimited) cache which is active between requests.

So let say we have this payload:

msg.payload = ["foo","bar"]

and we sent it twice to a 'debug'-machine using two button-presses on a 'inject'-machine

the output of the first mousepress will be:


and the second mousepress:


(because the message was seen before and stored in the cache)

[{"id":"5795e277.a86a1c","type":"inject","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"x":116,"y":640,"z":"886b17b1.7794e8","wires":[["85b26b47.7a4d98"]]},{"id":"d0d04ab0.2f2fb8","type":"debug","name":"","active":true,"console":"true","complete":"false","x":680,"y":639,"z":"886b17b1.7794e8","wires":[]},{"id":"b0d6e4a1.4f2918","type":"function","name":"filter new items","func":"// this machine will delete items which have been seen already\n// please the following id unique\nvar cacheid = \"foo-bar-cache\";\n\n// prepare cache\nvar enabled = true;\nvar now     = new Date().getTime();\nvar old     = now;- ( (60 * 60) * 24 ); // now-1 day\nif( == undefined ) = {};\nvar cache =;\nif( cache[cacheid] == undefined ) cache[cacheid] = {};\n\n// loop thru items and delete if seen before\nvar items = msg.payload;\nfor( i in items ){\n  var jsonstr = JSON.stringify( msg.payload[i] );\n  if( cache[cacheid][jsonstr] != undefined && enabled) delete msg.payload[i];\n  else cache[cacheid][jsonstr] = now;\n}\n\nfor( i in cache[cacheid] ) // cleanup cache\n  if( cache[cacheid][i] < old ) delete cache[cacheid][i];\n\ = cache;\n\nreturn msg;","outputs":1,"x":489,"y":639,"z":"886b17b1.7794e8","wires":[["d0d04ab0.2f2fb8"]]},{"id":"85b26b47.7a4d98","type":"function","name":"dummy data","func":"\nmsg.payload = [\"foo\",\"bar\"];\nreturn msg;","outputs":1,"x":293,"y":639,"z":"886b17b1.7794e8","wires":[["b0d6e4a1.4f2918"]]}]

Flow Info

created 2 years, 9 months ago

Node Types

  • debug (x1)
  • function (x2)
  • inject (x1)


  • cache
  • filter
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