# How to create and call global functions?

**URL:** <https://community.homey.app/t/how-to-create-and-call-global-functions/104302>\
**Category:** Questions & Help\
**Created:** [February 18, 2024, 3:47pm UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302 "2024-02-18T15:47:14Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![vletroye](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/vletroye/32/101044_2.png) [@vletroye](https://community.homey.app/u/vletroye)\
**Post date:** [February 18, 2024, 3:47pm UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/1 "2024-02-18T15:47:14Z")

</div>

Hello,

I probably didn’t yet fully get the philosophy of Homey… but I want to write a function XYtoRGB and don’t really find how to do this properly with Homey.

The function will to convert into an RGB string any input ‘Philips hue scene’ (represented by it’s x, y colors and brillance). Obviously, I don’t want to type its code in all my flows.

So far, I found that I could probably use an HomeyScript like this:

```auto
//args[0] = '{ "x":0.5019, "y":0.4152, "bri":143 }';

if (args[0] === '' || args[0] === undefined) {
  throw new Error('This script needs a json as parameter: { "x":0.561, "y":0.4042, "bri":90 }');
}

const flow_args = JSON.parse(args[0]);
if (Object.keys( flow_args).length != 3) {
  throw new Error('This script has only ' + Object.keys( flow_args).length + ' parameters and needs 3. Ex.: { "x":0.561, "y":0.4042, "bri":90 } ');
}

console.log('x:' + flow_args.x );
console.log('y:' + flow_args.y );
console.log('bri:' + flow_args.bri );

const x = (typeof flow_args.x === 'number')
  ? flow_args.x
  : 0.561;
const y = (typeof flow_args.y === 'number')
  ? flow_args.y
  : 0.4042;
const bri = (typeof flow_args.bri === 'number')
  ? flow_args.bri
  : 90;

z = 1.0 - x - y;

Y = bri / 255.0; // Brightness of lamp
X = (Y / y) * x;
Z = (Y / y) * z;
r = X * 1.612 - Y * 0.203 - Z * 0.302;
g = -X * 0.509 + Y * 1.412 + Z * 0.066;
b = X * 0.026 - Y * 0.072 + Z * 0.962;
r = r <= 0.0031308 ? 12.92 * r : (1.0 + 0.055) * Math.pow(r, (1.0 / 2.4)) - 0.055;
g = g <= 0.0031308 ? 12.92 * g : (1.0 + 0.055) * Math.pow(g, (1.0 / 2.4)) - 0.055;
b = b <= 0.0031308 ? 12.92 * b : (1.0 + 0.055) * Math.pow(b, (1.0 / 2.4)) - 0.055;
maxValue = Math.max(r,g,b);
r /= maxValue;
g /= maxValue;
b /= maxValue;
r = r * 255; if (r < 0) { r = 255 };
g = g * 255; if (g < 0) { g = 255 };
b = b * 255; if (b < 0) { b = 255 };

r = Math.round(r).toString(16);
g = Math.round(g).toString(16);
b = Math.round(b).toString(16);

if (r.length < 2)
    r="0"+r;        
if (g.length < 2)
    g="0"+g;        
if (b.length < 2)
    b="0"+r;        
rgb = "#"+r+g+b;

console.log(args[0] + ' = ' + rgb);
return rgb;

```

Unfortunately, I don’t see how to call it properly from a flow.  
I tried with a HomeScript’s card "Run … with argument’

![image](https://us1.discourse-cdn.com/flex025/uploads/athom/original/3X/f/e/fe338e6874384a6b5c2c11de49c73b065e365d05.png)

But first, I struggled to pass an array of parameters. I read on this forum that people recommend using splitting the single input argument or use a json string… Really no other way ? I guess there is some trick with the notation (ex.: {{ [0.40, 0.3605, 80] }]) ? indeed, the HomeScript documentation is clearly mentioning an array :

![image](https://us1.discourse-cdn.com/flex025/uploads/athom/original/3X/b/4/b4e7ca5e5acfdb5fcff55cdc64fb1d3f12a1a12b.png)

And next, I can’t find how to retrieve the result. I read also on this forum that one could create and set a tag with the output value. But I don’t want to define one distinct tag per flow where I use this script 😕 Maybe I am not using/calling correctly my HomeyScript ??

Any advice for me to achieve my purpose ?  
Thx a lot in adv for any tip !

V.

---

<div class="post-metadata">

**Author:** ![Heronimus](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/heronimus/32/3564_2.png) [@Heronimus](https://community.homey.app/u/Heronimus)\
**Post date:** [December 3, 2025, 1:46pm UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/2 "2025-12-03T13:46:02Z")

</div>

I’m finding a way to create something simular; a formula (HomeyScript?) which calculates a value on given parameters. Maybe you (@vletroye) did find a way, or someone else here has good ideas?

I would appreciate. Thanks in advance.

---

<div class="post-metadata">

**Author:** ![Ben\_van\_der\_Beek](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/ben_van_der_beek/32/146747_2.png) [@Ben\_van\_der\_Beek](https://community.homey.app/u/Ben_van_der_Beek)\
**Post date:** [December 3, 2025, 3:43pm UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/3 "2025-12-03T15:43:24Z")

</div>

A somewhat ambiguous question. What exactly do you want to calculate? If it’s a simple calculation, the “Calculate Number Variable as Text” logic card might work in a flow. If it’s more complex, you could do it in HomeyScript, but then the question is: do you have any JavaScript skills?

---

<div class="post-metadata">

**Author:** ![Heronimus](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/heronimus/32/3564_2.png) [@Heronimus](https://community.homey.app/u/Heronimus)\
**Post date:** [December 3, 2025, 5:50pm UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/4 "2025-12-03T17:50:42Z")

</div>

Hi Ben,

It is a simple formula to calculate value in a transition flow. Like setting dim- or volume values in a fading flow.

x=start value  
y=end value  
z1=current second  
z2=total of seconds

result=x+(ABS(z2-z1)\*((y-x)/z2)

I’m finding a way to do this with Homeyscript, like vletroye is trying to do.

---

<div class="post-metadata">

**Author:** ![Ben\_van\_der\_Beek](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/ben_van_der_beek/32/146747_2.png) [@Ben\_van\_der\_Beek](https://community.homey.app/u/Ben_van_der_Beek)\
**Post date:** [December 5, 2025, 9:16am UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/5 "2025-12-05T09:16:48Z")

</div>

Of course, I don’t know in which context/flow you want to use this calculation, but this might help.

This is the calculation in the form of a Homeyscript function that returns the result.

`// Async HomeyScript function to calculate progress value`  
`async function calculateProgress(startValue, endValue, currentSecond, totalSeconds) {`  
`// Ensure inputs are numbers`  
`const x = Number(startValue);`  
`const y = Number(endValue);`  
`const z1 = Number(currentSecond);`  
`const z2 = Number(totalSeconds);`  
`const result = x + (Math.abs(z2 - z1) * ((y - x) / z2));`  
`return result;`  
`}`

Usage: const myVar = await calculateProgress(10, 100, 30, 60);

You could also, of course, use the “calculate variable as text” logic card in a flow and paste the formula within the {{ }} brackets. This would result in this:

 ![progress-logic-card](https://us1.discourse-cdn.com/flex025/uploads/athom/original/3X/7/d/7dbf7cb806e0f52d6d23c71a149bf6e4082eb544.jpeg)

The parameters used must offcourse already exist in the flow as tags, and you must have a named variable to store the result.

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<div class="post-metadata">

**Author:** ![robertklep](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/robertklep/32/160628_2.png) [@robertklep](https://community.homey.app/u/robertklep)\
**Post date:** [December 5, 2025, 9:23am UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/6 "2025-12-05T09:23:41Z")

</div>

What’s the purpose of marking the function as being async when it does nothing asynchronous?

---

<div class="post-metadata">

**Author:** ![Ben\_van\_der\_Beek](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/ben_van_der_beek/32/146747_2.png) [@Ben\_van\_der\_Beek](https://community.homey.app/u/Ben_van_der_Beek)\
**Post date:** [December 5, 2025, 9:51am UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/7 "2025-12-05T09:51:19Z")

</div>

Right, Robert, it’s a bit of a habit, as an await statement is often needed within a function. But it doesn’t hurt here, it’s just an example. I also haven’t fully understood the context in which it should be used.

---

<div class="post-metadata">

**Author:** ![robertklep](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/robertklep/32/160628_2.png) [@robertklep](https://community.homey.app/u/robertklep)\
**Post date:** [December 5, 2025, 10:07am UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/8 "2025-12-05T10:07:12Z")

</div>

If `await` is being used inside a function (or you _want_ to use it), it should be marked `async` 🙂

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<div class="post-metadata">

**Author:** ![Ben\_van\_der\_Beek](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/ben_van_der_beek/32/146747_2.png) [@Ben\_van\_der\_Beek](https://community.homey.app/u/Ben_van_der_Beek)\
**Post date:** [December 5, 2025, 10:14am UTC](https://community.homey.app/t/how-to-create-and-call-global-functions/104302/9 "2025-12-05T10:14:33Z")

</div>

I know. Async isn’t necessary here. But it doesn’t hinder anything. The point is the calculation example within a function. If it’s even necessary to use HomeyScript at all. Depends on the context.