ADAM / AIAHTML5

function pad ( num, len ) {
	let result = String( num );
	return result + repeat( ' ', len - result.length );
}

function repeat ( str, times ) {
	let result = '';
	while ( times-- ) result += str;
	return result;
}

export default function getSnippet ( source, loc, length = 1 ) {
	const first = Math.max( loc.line - 5, 0 );
	const last = loc.line;

	const numDigits = String( last ).length;

	const lines = source.split( '\n' ).slice( first, last );

	const lastLine = lines[ lines.length - 1 ];
	const offset = lastLine.slice( 0, loc.column ).replace( /\t/g, '  ' ).length;

	let snippet = lines
		.map( ( line, i ) => `${pad( i + first + 1, numDigits )} : ${line.replace( /\t/g, '  ')}` )
		.join( '\n' );

	snippet += '\n' + repeat( ' ', numDigits + 3 + offset ) + repeat( '^', length );

	return snippet;
}