The following sections are cited from https://momentjs.com/docs/#/displaying/ for Date and Time formatting and http://www.gwtproject.org/ for Number formatting. 

Formatting Date and Time

Patterns

Localized Formats

Because preferred formatting differs based on locale, there are a few tokens that can be used to format a moment based on its locale.

There are upper and lower case variations on the same formats. The lowercase version is intended to be the shortened version of its uppercase counterpart.

Escaping Characters

To escape characters in format strings, you can wrap the characters in square brackets.

moment().format('[today] dddd'); // 'today Sunday'

Formatting Numbers

Patterns

Formatting is based on customizable patterns that can include a combination of literal characters and special characters that act as placeholders and are replaced by their localized counterparts. Many characters in a pattern are taken literally; they are unchanged during formatting. Special characters, on the other hand, stand for other characters, strings, or classes of characters. For example, the '#' character is replaced by a localized digit.

Often the replacement character is the same as the pattern character. In the U.S. locale, for example, the ',' grouping character is replaced by the same character ','. However, the replacement is still actually happening, and in a different locale, the grouping character may change to a different character, such as '.'. Some special characters affect the behavior of the formatter by their presence. For example, if the percent character is seen, then the value is multiplied by 100 before being displayed.

The characters listed below are used in patterns. Localized symbols use the corresponding characters taken from corresponding locale symbol collection. To insert a special character in a pattern as a literal (that is, without any special meaning) the character must be quoted. There are some exceptions to this which are noted below.

If there is a semicolon in the pattern, then the first part (subpattern) is for positive values and the second is for negative ones, e.g. "#,##0.00;(#,##0.00)". Each subpattern has a prefix, a numeric part, and a suffix. If there is no explicit negative subpattern, the negative subpattern is the localized minus sign prefixed to the positive subpattern. That is, "0.00" alone is equivalent to "0.00;-0.00". If there is an explicit negative subpattern, it serves only to specify the negative prefix and suffix; the number of digits, minimal digits, and other characteristics are ignored in the negative subpattern. That means that "#,##0.0#;(#)" has precisely the same result as "#,##0.0#;(#,##0.0#)".

The prefixes, suffixes, and various symbols used for infinity, digits, thousands separators, decimal separators, etc. may be set to arbitrary values, and they will appear properly during formatting. However, care must be taken that the symbols and strings do not conflict, or parsing will be unreliable. For example, the decimal separator and thousands separator should be distinct characters, or parsing will be impossible.

The grouping separator is a character that separates clusters of integer digits to make large numbers more legible. It commonly used for thousands, but in some locales it separates ten-thousands. The grouping size is the number of digits between the grouping separators, such as 3 for "100,000,000" or 4 for "1 0000 0000".

Pattern Grammar (BNF)

The pattern itself uses the following grammar:

Notation:

The first subpattern is for positive numbers. The second (optional) subpattern is for negative numbers.