Re: [node-red] FLIP-FLOP

[Colin Law]

You could write a simple function node that uses a node context
variable to remember the current state and flip it each time a message
is received.

Colin

On 1 May 2017 at 01:39, David Caparrós <davi...@gmail.com> wrote:
> can someone help me? I need a flip-flop funcion to use an input to tiger 0
> or 1 each time the input is received, a simple flip flop function that i'm
> so estupid that i'm not able to find.
>
> Thanks in advance
>
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[steve rickus]

Sounds like a job for 'modulo' -- in javascript the percent sign is used to return the remainder of dividing a number by another number:

var odd = 5 % 2; // returns 1
var even = 6 % 2; // returns 0
var flipflop = counter % 2; // assuming you are keeping a count of msg received

There are many ways to keep track of the number of messages received -- search the flows library for the word "count", for example. Many people write their own little function node that gets the counter from the node's context (or uses 0 if not defined), then increment the value and save it back to context:

var count = context.get("counter") || 0;
count++;
context.set("counter", count);
msg.payload = count % 2;
return msg;

I usually keep a browser open to the Mozilla Developer Network and the W3 Schools sites as my javascript reference...

[Colin Law]

I would prefer to do

var count = context.get("counter") || 0;

count = (count+1) % 2;
context.set("counter", count);
msg.payload = count;
return msg;

That stops it failing when the value of count gets too large after a
few billion years.

Colin

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