Some shims don’t guard against Object.prototype modifications

[mathiasbynens]

Add this to the tests:

Object.prototype[1] = 42; // try to break `arguments[1]`
Object.prototype[2] = 'lol'; // try to break `arguments[2]`

Functions and methods that might have this issue:

• Array: from, fill, find, findIndex
• String: startsWith, endsWith, contains

[paulmillr]

Is it a real concern or hasOwnProperty usage is in the spec?

[mathiasbynens]

The spec for e.g. String#startsWith says:

Step 7. Let pos be ToInteger(position). (If position is undefined, this step produces the value 0).

Luckily, there’s no need to use hasOwnProperty to detect if a secondary argument was passed or not.

I had the same problem with my polyfill. Here’s the fix: mathiasbynens/String.prototype.startsWith@978e0c2