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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
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@DrAzzy
I2C addresses (like 0x63) are hexadecimal (base 16). You can use the number represented as base 10 or hexadecimal (or binary, ie, 0b01100011) interchangably.
ie, 0x63 evaluates to 99 - you can do I2C1.sendTo(0x63,...) or I2C1.sendTo(99,...) - they're exactly the same. Which format you use matters only for the purposes of code readability. (in fact, if you use the code minification option, it converts all the hexadecimal values in your code to decimal, since that saves 1-2 bytes of code size per instance)
I2C1.readFrom() returns an array of bytes. When you do I2C1.readFrom(99,10), that will request 10 bytes from the device, returning them as an array of 10 bytes. It's up to you to turn that array into something meaningful. A "null" is probably a byte with a value of 0.
You can find a lot of examples of using I2C in the source code for the modules ( http://espruino.com/modules ). Also, have you read the reference, or just the tutorial? The reference ( http://espruino.com/Reference ) is a great resource, and I think it would have answered at least the question about the format data is returned
As to why one would use it, it's because it's easy to convert between binary and hexadecimal in your head. It's a real help when you're writing code to control a device where you need to send one byte where each bit sets some feature.