node_modules/css-tree/lib/common/SyntaxError.js

var createCustomError = require('../utils/createCustomError');
var MAX_LINE_LENGTH = 100;
var OFFSET_CORRECTION = 60;
var TAB_REPLACEMENT = '    ';

function sourceFragment(error, extraLines) {
    function processLines(start, end) {
        return lines.slice(start, end).map(function(line, idx) {
            var num = String(start + idx + 1);

            while (num.length < maxNumLength) {
                num = ' ' + num;
            }

            return num + ' |' + line;
        }).join('\n');
    }

    var lines = error.source.split(/\r\n?|\n|\f/);
    var line = error.line;
    var column = error.column;
    var startLine = Math.max(1, line - extraLines) - 1;
    var endLine = Math.min(line + extraLines, lines.length + 1);
    var maxNumLength = Math.max(4, String(endLine).length) + 1;
    var cutLeft = 0;

    // column correction according to replaced tab before column
    column += (TAB_REPLACEMENT.length - 1) * (lines[line - 1].substr(0, column - 1).match(/\t/g) || []).length;

    if (column > MAX_LINE_LENGTH) {
        cutLeft = column - OFFSET_CORRECTION + 3;
        column = OFFSET_CORRECTION - 2;
    }

    for (var i = startLine; i <= endLine; i++) {
        if (i >= 0 && i < lines.length) {
            lines[i] = lines[i].replace(/\t/g, TAB_REPLACEMENT);
            lines[i] =
                (cutLeft > 0 && lines[i].length > cutLeft ? '\u2026' : '') +
                lines[i].substr(cutLeft, MAX_LINE_LENGTH - 2) +
                (lines[i].length > cutLeft + MAX_LINE_LENGTH - 1 ? '\u2026' : '');
        }
    }

    return [
        processLines(startLine, line),
        new Array(column + maxNumLength + 2).join('-') + '^',
        processLines(line, endLine)
    ].filter(Boolean).join('\n');
}

var SyntaxError = function(message, source, offset, line, column) {
    var error = createCustomError('SyntaxError', message);

    error.source = source;
    error.offset = offset;
    error.line = line;
    error.column = column;

    error.sourceFragment = function(extraLines) {
        return sourceFragment(error, isNaN(extraLines) ? 0 : extraLines);
    };
    Object.defineProperty(error, 'formattedMessage', {
        get: function() {
            return (
                'Parse error: ' + error.message + '\n' +
                sourceFragment(error, 2)
            );
        }
    });

    // for backward capability
    error.parseError = {
        offset: offset,
        line: line,
        column: column
    };

    return error;
};

module.exports = SyntaxError;