Expand evaluation of global built-ins in @babel/traverse

[lorenzoferre]

Q	A
Fixed Issues?
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?	Yes
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

Evaluation of global built-ins includes btoa and atob. Before this pull request path.evaluate() of isFinite, isNaN, parseFloat, parseInt, encodeURI, decodeURI, encodeURIComponent and decodeURIComponent were possibile only with keywords String or Number before the method name (Number.parseInt("1");).
An example of this new feature:

const oldTraverse = require("@babel/traverse").default;
const newTraverse = require("../babel/packages/babel-traverse/lib").default;
const babel = require("@babel/core");

const code = "parseInt('1');";

var ast = babel.parse(code);

oldTraverse(ast, {
  CallExpression(path) {
    let evaluated = path.evaluate();
    console.log(`confident old traverse: ${evaluated.confident}`);
  }
});

newTraverse(ast, {
  CallExpression(path) {
    let evaluated = path.evaluate();
    console.log(`confident new traverse: ${evaluated.confident}`);
    console.log(`value new traverse: ${evaluated.value}`);
  }
});

This code produces:

confident old traverse: false
confident new traverse: true
value new traverse: 1

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/54988/

[lorenzoferre]

There is no backwards compatibility with older versions of node due to operators like ?., ||= and so on inside the packages/babel-traverse/lib files.

[JLHwung]

operators like ?., ||= and so on inside the packages/babel-traverse/lib files.

If you mean you have spotted them on your local environment, we compile src to lib targeting the current node version, i.e. the node version you are using locally, which probably supports these operators. On CI, we will compile src targeting Node.js 6.9, the minimum Node version Babel 7 (still) supports.

[lorenzoferre]

@JLHwung You are right, I'm a newbie with node.
The problem was that the btoa and atob functions are available from version 16 onwards.

[lorenzoferre]

@JLHwung this is my first time making a pull request, so do I need to do anything else before someone reviews my code?

[JLHwung]

btoa and atob functions are available from version 16 onwards.

You are right. In that case we should postpone the support otherwise path.evaluate() will return different results on different node versions.

[liuxingbaoyu]

Can you add a test that might throw an exception? For example atob("a")

[lorenzoferre]

btoa and atob functions are available from version 16 onwards.

You are right. In that case we should postpone the support otherwise path.evaluate() will return different results on different node versions.

I hadn't thought of doing a version check on node.
I did this check, and if the version is greater than 16, then the btoa and atob functions are added to the VALID_IDENTIFIER_CALLEES array. I also updated the tests.

[lorenzoferre]

Can you add a test that might throw an exception? For example atob("a")

path.evaluate() of btoa and atob produces undefined if the node version is lower than 16, so I updated the tests with this undefined check.
If, on the other hand, one tries from the node console to use btoa or atob, it throws an Uncaught ReferenceError exception, but I wouldn't know how to test throwing the exception.

[lorenzoferre]

@JLHwung I also have updated the btoa and atob tests.
I think they are cleaner than the old version.

[lorenzoferre]

@JLHwung Sorry for my many questions but now this pull request could be merged?
Because I don't know how the flow of these kind of operation works.

[nicolo-ribaudo]

We have a two-approval policy for merging PRs.

I do not feel strongly in favor of this, but the added maintenance cost is basically zero and it just expands an existing feature 👍

[nicolo-ribaudo]

Actually, since this is a new feature it should be landed in a minor version (7.23.0). You will have to wait a bit before that this PR is merged (probably ~1 month? maybe less, you can track progress by seeing which PRs in https://github.com/babel/babel/milestone/57 have the two approvals), but there is nothing else that you need to do :)

[lorenzoferre]

All right, thank you very very much @JLHwung and @nicolo-ribaudo for everything. As a I said before this is my first pull request so I didn't know if I needed do anything else and I'm sorry for my many questions.
I'm very glad to contribute to a project like this.
I made this pull request because I'm using babel in my thesis project about automating the javascript deobfuscation process via abstract syntaxt trees. In this scenario it's very common to find operations like parseInt, parseFloat etc. in obfuscated code.

[nicolo-ribaudo]

That's awesome :) If you are graduating in September and you are mentioning this PR in your thesis, we can make sure to release it by then.

[lorenzoferre]

That's awesome :) If you are graduating in September and you are mentioning this PR in your thesis, we can make sure to release it by then.

Yeah, I should graduate on 28 or 29 September or 2 October.
Certainly, if there is the possibility of mentioning this pull request I am more than happy and I do it very willingly.

[nicolo-ribaudo]

We'll release today, sorry for this being so last-minute :)

[lorenzoferre]

We'll release today, sorry for this being so last-minute :)

That's fantastic.
You don't sweat it, I'm in time.
I really appreciate that you released this version before my graduation.