Refactor Array.prototype.insert function

[Avalonalan]

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Describe the bug

Even if for-in loop is not recommanded, there are still some people using it.
If someone use for-in loop to loop an empty array, there an error happens. Because
javascript object is prototype chain, enumerable properties are also looped over when an
empty array is looped over.

Information

• OS: Windows 10
• Browser: Chrome (Latest)
• Extensions: Json viewer, Page ruler, and Language tool.
• Version: 79.0.3945.130 (Official Build) (64-bit)

Additional context
It also occurs when I use IE, Edge.