Several efficient and concise character handler functions-javascript skills

Several efficient and concise character processing functions are extended based on String. prototype:
The reason is that a netizen discussed two functions with me,
One is isDateTime (judge whether the character Meets the yyyy-mm-dd hh: mm: ss Date Format)
The other is the left function, which is similar to the left function of vbscript to achieve mixed interception of Chinese and English characters.
Both of these functions use loops and N-plus if statements. Each function has more than 40 lines of code and can be simplified.
As a result, I wrote the following code. I dare not say it is the most efficient, but it is enough to simplify it. The left function is only one line.

The Code is as follows:

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