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Formatted Values in Heatmap

Hello, I would like to be able to format the values shown in my heatmap, for example for a given cell with a value of 500,000 I would like to show 500k and so forth.
I am willing to write some javascript and i have even seen in the app's source code that there is a format propertie that i could use.

How could i accomplish this customization ?

I appreciate any help given.