Variable i gets reset to 0

[zznidar]

JavaScript variable i is reset to 0 after incrementing it by 1 on an xmlhttp.onprogress (onerror) event. If it is given a different name, test for example, it is not reset to 0.

In Chrome 71.0.3578.99 for Android and Chrome, Firefox, Edge for Windows, variables are incremented regardless of the name.

Demo:
https://zznidar.github.io/bugreports/Firefox%20Focus/Variable%20i%20gets%20reset%20to%200/

Source code:
index.html: https://raw.githubusercontent.com/zznidar/bugreports/master/Firefox%20Focus/Variable%20i%20gets%20reset%20to%200/index.html
runtime.js: https://raw.githubusercontent.com/zznidar/bugreports/master/Firefox%20Focus/Variable%20i%20gets%20reset%20to%200/runtime.js

Steps to reproduce

1. Visit https://zznidar.github.io/bugreports/Firefox%20Focus/Variable%20i%20gets%20reset%20to%200/
2. Press the "Begin" button (Note: make sure JavaScript is enabled)
3. Wait a few seconds for an alert to appear
4. Press the "Begin" button again
5. Wait for another alert. Compare variables i and test

Expected behavior

Each variable, regardless of its name, should be incremented when variable++ is executed in js-code. Thus, both i and test should be increased by 1 each time an alert pops up.

Actual behavior

Variable named i is reset to 0 each cycle, hence the alert always outputs it as 1. Variable test increments as expected.

Device information

• Android device: pocophone f1, Android 8.1

• Focus version: 8.0.4

• Android device: Samsung Galaxy S8+, Android 8.0

• Focus version: 7.0.13

[colintheshots]

Which user agent is this happening with? Could you please send us the result of "focus:about"?

[zznidar]

user agent:
Mozilla/5.0 (Linux; Android 8.1.0) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Focus/8.0.4 Chrome/71.0.3578.99 Mobile Safari/537.36

focus:about

8.0.4 (Build #323512256)

Firefox Focus puts you in control.

Use it as a private browser:

Search and browse right in the app
Block trackers (or update settings to allow trackers)
Erase to delete cookies as well as search and browsing history
Firefox Focus is produced by Mozilla. Our mission is to foster a healthy, open Internet.
Learn more

Second device (SGS8+):
user agent:
Mozilla/5.0 (Linux; Android 8.0.0) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Focus/7.0.13 Chrome/71.0.3578.99 Mobile Safari/537.36

focus:about
7.0.13 (Build #323021954)

Firefox Focus puts you in control.

Use it as a private browser:

Search and browse right in the app
Block trackers (or update settings to allow trackers)
Erase to delete cookies as well as search and browsing history
Firefox Focus is produced by Mozilla. Our mission is to foster a healthy, open Internet.
Learn more

[colintheshots]

You're right. This is our fault and it's limited to WebView. It's caused by inserted JS polluting the namespace. We're moving to GeckoView soon, so we need to decide if we should fix this directly or simply change engines to fix it. Don't worry, we're on it.

focus-android/app/src/main/java/org/mozilla/focus/webview/FocusWebViewClient.java

Line 100 in 9827c02

"for (i = 0; i < links.length; i++) {" +

[cpeterso]

 "for (i = 0; i < links.length; i++) {" +

Can this bug be fixed by simply declaring let i in the loop head? The current code is implicitly using a global variable i. Breaking web content could cause some pretty bad problems.

This typo would cause an exception if this code used JS use strict mode.

[niftylettuce]

I had the same issue, I was using underscore.string globally in window and the global s variable was getting reset to 0 instead of being an object with methods like s.isBlank.

Using latest version of Firefox Klar

Ref: https://github.com/epeli/underscore.string

[niftylettuce]

To clarify - I am still having this issue on latest versions.