keyTap doesn't work with capital letters.

[octalmage]

This code doesn't work:

var robot = require("robotjs");
robot.keyTap("H");

but this does:

var robot = require("robotjs");
robot.keyTap("h");

This also works:

var robot = require("robotjs");
robot.typeString("H");

[octalmage]

This is because keyTap is build for holding keys down with modifiers (like shift or ctrl). To do a capital letter you'd press h with shift.