Regex to check if the first character is uppercase

I'm trying to check that the first character of a username is capital, the following can be letters or numbers and at most 20 characters long. Can someone explain why my syntax is wrong?

/^[A-z][a-z0-9_-]{3,19}$/

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你的第一个Z不是大写Z.

/^[A-Z][a-z0-9_-]{3,19}$/

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Your first character needs to be AZ , not Az

So

/^[Az][a-z0-9_-]{3,19}$/

Should be

/^[AZ][a-z0-9_-]{3,19}$/

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我会这样做：

var firstChar = strToCheck.substring(0, 1);

if (firstChar == firstChar.toUpperCase()) {
    // it is capital :D
}

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