FormatFloat mask

I'm using FormatFloat and passing this #, ## 0.00 mark.
It is formatting this way 1,000.00
and you should format 1,000.00 like this, because this is how you format it in VCL and FMX. How do I put this format?

I'm sorry but I do not understand what you write.

What exactly is

"passing this #, ## 0.00 mark"

Do you set the mask as #,## 0.00 , do you set the mask as #,## and pass value 0.00?

So, please inform what exact code you execute and what exact result you get.

The mask is #, ## 0.00
I'm using it like this: FormatFloat ('#, ## 0.00', 1000)
The result I get is 1,000.00 and the result I need is 1.000,00

While this is pas2js RTL, this is expected to depend on your FormatSettings.DecimalSeparator / FormatSettings.ThousandSeparator.
And FormatSettings.DecimalSeparator / FormatSettings.ThousandSeparator is browser locale dependent.