Awk-compatible implementation of strftime() function in JavaScript

strftime.js

function strftime( tmpl, timestamp )
{
	let regex = /%([admbyYzZHMS])/g;
	let date = new Date( ( timestamp + 60 * getTimezone( ) ) * 1000 );
	let utc_format = date.toUTCString( );  // Tue, 12 May 2020 23:50:21 GMT
	let iso_format = date.toISOString( );  // 2020-05-12T23:50:21.817Z
	
	return tmpl.replace( regex, function ( exp, type )
	{
		if( exp == '%%' )
			return '%';
			
		switch( type ) {
			case 'a':
				return utc_format.substr( 0, 3 );
			case 'd':
				return iso_format.substr( 8, 2 );
			case 'm':
				return iso_format.substr( 5, 2 );
			case 'b':
				return utc_format.substr( 8, 3 );
			case 'y':
				return iso_format.substr( 2, 2 );
			case 'Y':
				return iso_format.substr( 0, 4 );
			case 'H':
				return iso_format.substr( 11, 2 );
			case 'M':
				return iso_format.substr( 14, 2 );
			case 'S':
				return iso_format.substr( 17, 2 );
		}		
	} )
}