🚀 go-pugleaf

I'm wondering what javascript command I should use if I want to change the caption on a button (I mean the text that is written on the button).

Here is a part of the code. Everything isn't showed:
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myPage = myDoc.pages[myTable.parent.parent.index - 1];
myGeoBounds = myPage.textFrames[0].geometricBounds;
var myBtn = myPage.buttons.add(undefined, undefined, undefined, {geometricBounds:[
    String(myGeoBounds[0] - 15) + "mm",
    String(myGeoBounds[1] + 10) + "mm",
    String(myGeoBounds[2] - 5) + "mm",
    String(myGeoBounds[3] + 40) + "mm"]});
-------------------

So, how do I change the text that is written on that button?
Thanks! :)