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Is there a way to make the version of V8 JavaScript that my google script uses constant?

A rookie here.
Messing with my google scripts projects I have found a strange thing, a method that I was using was strike-through in the editor and it looked like this --> substr . Researching, I found that it is because this method is being deprecated. And for people looking how to solve it look the documentation in developer.mozilla.org.
At first, I had no problem with this, but, if it was not there before, and it is now, that means that the version of javascript that my project is using is changing and I do not want that. And there is my question
Is there a way to make the version of V8 JavaScript that my google script uses constant?
Looking in to the app-scripts documentation I have found that it uses V8 and that it is defined in the manifest but the way of freezing to a certain version is nowhere to be found. Maybe there is an easy answer, but I have no clue where else to look. Any help will be welcomed.

No, there is no way to select a particular V8 version for your GAS.
That said, JavaScript engines are generally very conscious of backwards compatibility. It is extremely rare that features are removed -- there are a good number of "legacy"/"deprecated" things in JS that won't be removed for the foreseeable future, because there's too much old and unmaintained (but still used) code out there that depends on them, and browser makers don't want to break that code.
Regarding the specific case at hand, I personally would be quite surprised if String.prototype.substr ever got removed. I see its deprecation as more of a "pro tip: how not to confuse substr and substring: only ever use one of them".
FWIW, V8 itself has no notion of deprecated JavaScript features. The strike-through you see is just an editor feature. Updating or not updating the V8 version underneath wouldn't affect it.
Taking a step back: writing software once and then expecting it to work without maintenance or monitoring for decades is, unfortunately, generally not a thing. For instance, if you developed a game for Windows 95, you'd have to expect that it won't run well (or not at all) on modern Windows versions. There are countless more examples of operating systems, SDKs/toolkits, compilers/engines, and programming languages themselves evolving over time in ways that guarantee backwards-compatibility for a couple of years but not forever. This is the flip side of technological progress. Pinning yourself to certain outdated versions is generally not a viable solution, for a variety of reasons.
So actually, in comparison, when you write an app or script in JavaScript, you have a very high chance of it still working fine 20 years later. So I wouldn't worry about it too much.

How to safely use ES6 new features?

There are many ES6 features that look great like => syntax, Map object, and a long etc.
To be honest I'm kind of tired of checking if there is support for addEventListener due to ie8 attachEvent, and I wouldn't like that kind of pain coming back to my life.
So how, would you deal with this new posibilities? (or how will you, lets say, in a year or so). Would you not use them for basic actions but to add another layer of extra functions? Would you use it just for apps that you know you will be running in browsers that support them? Would you wait untill there is at least 90% of support?
I understand these are great features but for short to medium term usage it seems that you'd need to double your code checking and fallbacking for support.
Any enlightment about this subject?
EDIT: Please, don't mark this as duplicate. Notice I'm not asking how to check for support, I'm asking if it is wise to start using it, or it is better to wait. I'm also asking if the support check is the best option, not how to do it, or if there are other ways to proced while designing your code.

tl;dr: Make use of transpilers and polyfills.
Whether or not you should use new features primarily depends on your target environment and how exactly you are using new features. E.g. if you are targeting only the latest browser version, then you won't have an issue. Have to support IE8? That could be more difficult.
In general though, you should start using new features as soon as possible, and make use of tools that help you with that.
There are two aspects to look at:
New APIs
New syntax constructs
APIs
New API's can often (but not always) be polyfilled. I.e. you include a library which checks whether certain parts of the API exist, e.g. Map, and provides an alternative implementation if it doesn't.
These alternative implements may not be 100% equivalent or may not be as performant as a native implementation, but I'd say they work for 95% for all use cases.
The nice thing about polyfills is that you will be automatically using the native browser implementation if it is available.
Syntax
Making use of new syntax constructs, such as arrow functions or classes, is a bit more complex (but not much). The biggest issue is that browsers who do not support the syntax cannot even evaluate your code. You can only send code to the browser that it can actually parse.
Fortunately many of the new syntax elements, such as arrow functions, are really just syntactic sugar for things that are already possible ES5. So we can convert ES6 code into their ES5 or even ES3 equivalent.
Several such tools, called transpilers, have emerged over the last one or two years. Note that the transpiler has to convert your code before it is sent to the browser. This means that instead of simply writing your JS file and directly include in your page, you need to have a build step that converts the code first (just like we have in other languages, like C or Java).
This is different from how we wrote JS a couple of years ago, but having a build step has become increasingly more accepted by the JS community. There are also many build tools that try to make this as painless as possible.
One drawback is, unlike with polyfills, that you won't magically be using the native features if they become available. So you could be stuck with shipping the transpiled version for a long time, until all your target environments support all the features you need. But that's probably still better than not using the new features at all.

You can use BabelJS or Google Traceur
You have to include in your build process a step to transform ES6, ES7 code to Javascript compatible with todays browsers. Like a gulp or grunt task. Babel has a list of supported tools here

How do you ensure compatibility JavaScript libraries for the browser and for node.js

I'm working with a team on a TypeScript librabry called Classical.js, and we would very much like the core module of this library to be JavaScript environment agnostic. In my mind, that means it should not only function correctly cross-browser, but also as a dependency in a node.js project.
First of all, am I missing any major JavaScript environments in my test matrix that I should be aware of?
Unfortunately no one on the team develops with node. Therefore we're not quite sure what APIs to avoid (obviously the DOM) to ensure compatibility. Are there are a standard set of GOTCHAs that node developers run into when using code that has only been tested in the browser?
One discrepancy that we did (hopefully) account for the name of the global scope, which, if memory serves me correctly, is represented by an object named global in node and window in the browser. These are the sort of GOTCHAs that we are looking for.

I think you have an important issue here, one that that's currently underexposed: you want to create an isomorphic library, and you want to know which libraries you depend on are isomorphic. I think it would be a good thing when isomorphic modules would be clearly marked as such in for example npm.
There is a nice blog on this topic here: http://nerds.airbnb.com/isomorphic-javascript-future-web-apps/
Basically, isomorphic libraries should only use functionality build in JavaScript the language itself (ES3, ES5, ES6, ...).
You should avoid anything related to the DOM (window, document, navigator, ...), as this is only available inside a browser environment.
Many core modules of node.js cannot be used in a browser (like file system, os, process, network, streams, etc). For many core modules there are browser safe versions available (for example for crypto and http). Browserify uses these versions when bundling a node.js app for use in the browser.
There are a lot of JavaScript engines out in the wild, implemented in all kind of languages like C, Java, Python, etc. Also running directly on hardware like Espruino. These engines may not be 100% compliant with the language specs. For example, I encountered one day that the JS engine in Java (I think it was Rhino) didn't like a variable to have the name boolean. In these cases I would argue that these engines should get better compliancy rather than you having to work around their bugs/limitations.
Anyway, there is an easy way to test whether your library is isomorphic: try to run it in both node.js and the 5 biggest browsers :)

QuickCheck for Javascript

Is there a version of quickcheck that works for Javascript and that is well maintained? I have found several such as check.js and claire, but none of them seem to support shrinking of failing test cases, which has always struck me as the most useful part of the whole problem.

I'm creator of jsverify. I'll try constantly to make it better, bug reports and feature requests are welcomed.
There are also a list of other javascript generative testing libraries in a readme. So far I haven't found any other good alternative to the jsverify.

I recently released https://github.com/dubzzz/fast-check
I built it in order to answer several limitations I encountered in the existing quickcheck implementations in JavaScript.
It comes natively with a shrink feature which can shrink even combination of arbitraries (the frameworks I tried were failing on oneof like arbitraries).
It also can generate large objects and arrays.
By default it tends to try smaller values first in order to detect trivial edge cases while it covers all the possible inputs in next runs.
Lots of other features are on-going or already available :)
Cheers,
Nicolas

I wrote quick_check.js, which has a nice library of generators. Shrinking is not there yet, but is planned.

There seems to be a dearth of good quickcheck-like testing tools in javascript. However they are to be better supported in typed languages, and in fact you can write your tests in one of those languages if you wish.
To avoid dealing with runtime interop, I'd recommend going with a language which compiles to JS and runs on node.js (eg: Purescript with purescript-quickcheck), or a java-based language using the Nashorn engine provided in Java 8, for example ScalaCheck. You could even use ghcjs and the original flavor of the quickcheck library!

Netscape Enterprise Server and Server-Side JavaScript (SSJS) vs Node.js

What are the major differences between the Netscape Enterprise Server implementation of Server-Side JavaScript (SSJS) and the node.js implementation?
Why did not Netscape's implementation gain attention while the node.js seems to be far more popular?

Back in 1999/2000, I used to work at a company that used Netscape Server and SSJS. I don't know how popular it was at the time, but from first hand experience, I can tell you that almost everything about it was terrible:
It was a giant pain to debug (any changes to source files, even static files, required full reloading of the application, which was not a fast operation)
A simple error (such as an uncaught exception) often would lead to catastrophic server failure. Somewhat amusingly, this is the default behavior of NodeJS, although it is much easier to get around this problem with Node.
Although the syntax was JavaScript, it failed to implement one key advantage of modern JavaScript: runtime interpretation. Server Side JS with Netscape Server required compilation before deployment, and therefore dictated a very slow development process.
It followed a multi-threaded execution model (rather than modern JS VMs, which are almost always event-loop based)
Possibly it's biggest weakness was a lack of asynchronous programming support. All IO operations were blocking, and as such it required a heavyweight multithreaded model to support multiple clients. The execution model was more similar to a J2EE container than to modern event driven JavaScript VMs (ie: V8). In my opinion, this is the number one thing that NodeJS gets right: the async philosophy is deeply embedded in the NodeJS development workflow and it is the key to its lightweight, event driven, extremely efficient concurrency model.
Just for giggles, here's a link to the SSJS reference guide from version 1.2 . Starting on page 21, you can see all the standard functions and synchronous APIs for file objects, database queries, etc...
My company ended up switching to ColdFusion shortly thereafter and never looked back.

The main difference would be the evolution of Javascript over the the past 15+ years. Node.js uses the V8 Javascript Engine which would be far more optimized for modern computers.
Wikipedia has a good list of the differences between various server-side JS solutions.
Here is a list of features for Netscape Enterprise Server - provides a good idea of what makes modern SSJS solutions much better.
Why did it not gain attention? Realistically, client-side JS has only recently started to become the standard for web development so it was unlikely anybody would have considered using it for server-side development when it wasn't even really widely adopted for it's original purpose. I say widely adopted in that previously it was always difficult to cater JavaScript solutions to all browsers.