@digitalocean/do-markdownit/util/find_attr.js

Markdown-It plugin for the DigitalOcean Community.

/*
Copyright 2022 DigitalOcean

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.

You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

'use strict';

/**
 * Find an attribute within a given element.
 *
 * @param {string} attr Name of the attribute to find.
 * @param {string} tag HTML opening tag to search within.
 * @returns {?{start: number, end: number}}
 * @private
 */
module.exports = (attr, tag) => {
    // Find where attrs start and end
    let start = tag.indexOf(' ');
    let end = -1;
    const tagEnd = tag.lastIndexOf('>');

    // Track some temp vars
    const quoteStack = [];
    let backslashes = 0;

    // Find the start
    for (; start < tagEnd; start += 1) {
        // Check we're still viable (can we fit the attr, plus a space before, the equals after, and two quotes)
        if (tagEnd - start < attr.length + 4) return null;

        // Handle a start match
        if (tag.slice(start, start + attr.length + 2) === ` ${attr}=`
            && (tag[start + attr.length + 2] === '"' || tag[start + attr.length + 2] === '\'')
            && quoteStack.length === 0) {
            // Reset backslashes to zero, as we know the current char is a space
            backslashes = 0;

            // We want to start exploring the end from after the attr's opening quote
            end = start + attr.length + 3;

            // Attempt to find the end
            for (; end <= tagEnd; end += 1) {
                // Handle the end
                if (tag[end] === tag[start + attr.length + 2]
                    && quoteStack.length === 0
                    && backslashes % 2 === 0) break;

                // Handle quote (if closing is inside quotes, we want to ignore)
                if ((tag[end] === '"' || tag[end] === '\'') && backslashes % 2 === 0) {
                    if (quoteStack[quoteStack.length - 1] === tag[end]) quoteStack.pop();
                    else quoteStack.push(tag[end]);
                    continue;
                }

                // Handle backslash (if quote is escaped by backslash, we want to ignore)
                if (tag[end] === '\\') backslashes += 1;
                else backslashes = 0;
            }

            // Increment end by one to be the next char
            end += 1;

            // We found the end, bam
            if (end <= tagEnd) break;

            // Reset the quote stack (it was empty when we entered this block)
            // and, continue hunting for a valid start
            quoteStack.splice(0, quoteStack.length);
        }

        // Handle quote (if closing is inside quotes, we want to ignore)
        if ((tag[start] === '"' || tag[start] === '\'') && backslashes % 2 === 0) {
            if (quoteStack[quoteStack.length - 1] === tag[start]) quoteStack.pop();
            else quoteStack.push(tag[start]);
            continue;
        }

        // Handle backslash (if quote is escaped by backslash, we want to ignore)
        if (tag[start] === '\\') backslashes += 1;
        else backslashes = 0;
    }

    // Increment start by one to be after the space
    start += 1;

    return { start, end };
};