The following is stated on the overview of Google Apps Script documentation page:
Google Apps Script is a scripting language based on JavaScript that lets you do new and cool things with Google Apps like Docs, Sheets, and Forms.
They should use a bigger typeface to make it more visible!
The keyword here is based on JavaScript because it does indeed use most of the JavaScript Version 1.6 (with some portions of Version 1.7 and Version 1.8) and its general syntax. But, it has so many other methods that knowing only JavaScript is clearly not sufficient to use it adequately.
I would even say that you can learn it step-by-step when you need it, looking for information on a specific item each time you use a new type of object.
In Chapter 1, Enhancing Spreadsheets, we looked at the very first function presented in this book using that method (if you remember). The following is the code that was used:
function myAgeInHours(){
var myBirthDate = new Date('1958/02/19...