excel-col-to-num.js

function colNameToNum(col) {
	let result = 0;
	let colName = col.toUpperCase();
	for (let i = 0; i < colName.length; i++) {
		// A=1, B=2, ... Z=26
		const charValue = colName.charCodeAt(i) - "A".charCodeAt(0) + 1;
		// Base-26 conversion
		result = result * 26 + charValue;
	}
	// Convert to 0-indexed
	return result - 1;
}
console.log(colNameToNum("AA")); // 26
console.log(colNameToNum("a")); // 0
console.log(colNameToNum("B")); // 1
console.log(colNameToNum("z")); // 25