gettext: javascript-format

 
 15.3.6 JavaScript Format Strings
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    Although JavaScript specification itself does not define any format
 strings, many JavaScript implementations provide printf-like functions.
 ‘xgettext’ understands a set of common format strings used in popular
 JavaScript implementations including Gjs, Seed, and Node.JS. In such a
 format string, a directive starts with ‘%’ and is finished by a
 specifier: ‘%’ denotes a literal percent sign, ‘c’ denotes a character,
 ‘s’ denotes a string, ‘b’, ‘d’, ‘o’, ‘x’, ‘X’ denote an integer, ‘f’
 denotes floating-point number, ‘j’ denotes a JSON object.