sheetjs/bits/81_fmttype.js

var abstime = /\[[HhMmSs]*\]/;
function fmt_is_date(fmt/*:string*/)/*:boolean*/ {
	var i = 0, /*cc = 0,*/ c = "", o = "";
	while(i < fmt.length) {
		switch((c = fmt.charAt(i))) {
			case 'G': if(isgeneral(fmt, i)) i+= 6; i++; break;
			case '"': for(;(/*cc=*/fmt.charCodeAt(++i)) !== 34 && i < fmt.length;) ++i; ++i; break;
			case '\\': i+=2; break;
			case '_': i+=2; break;
			case '@': ++i; break;
			case 'B': case 'b':
				if(fmt.charAt(i+1) === "1" || fmt.charAt(i+1) === "2") return true;
				/* falls through */
			case 'M': case 'D': case 'Y': case 'H': case 'S': case 'E':
				/* falls through */
			case 'm': case 'd': case 'y': case 'h': case 's': case 'e': case 'g': return true;
			case 'A': case 'a':
				if(fmt.substr(i, 3).toUpperCase() === "A/P") return true;
				if(fmt.substr(i, 5).toUpperCase() === "AM/PM") return true;
				++i; break;
			case '[':
				o = c;
				while(fmt.charAt(i++) !== ']' && i < fmt.length) o += fmt.charAt(i);
				if(o.match(abstime)) return true;
				break;
			case '.':
				/* falls through */
			case '0': case '#':
				while(i < fmt.length && ("0#?.,E+-%".indexOf(c=fmt.charAt(++i)) > -1 || (c=='\\' && fmt.charAt(i+1) == "-" && "0#".indexOf(fmt.charAt(i+2))>-1))){/* empty */}
				break;
			case '?': while(fmt.charAt(++i) === c){/* empty */} break;
			case '*': ++i; if(fmt.charAt(i) == ' ' || fmt.charAt(i) == '*') ++i; break;
			case '(': case ')': ++i; break;
			case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9':
				while(i < fmt.length && "0123456789".indexOf(fmt.charAt(++i)) > -1){/* empty */} break;
			case ' ': ++i; break;
			default: ++i; break;
		}
	}
	return false;
}
SSF.is_date = fmt_is_date;