@digitalocean/do-markdownit/util/find_tag_open.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 the opening tag for a given tag name.
 *
 * @param {string} tag Name of the tag to find.
 * @param {string} html HTML snippet to search within.
 * @returns {?{start: number, end: number}}
 * @private
 */
module.exports = (tag, html) => {
    // Find the start of the tag
    const start = html.indexOf(`<${tag}`);
    if (start === -1) return null;
    let end = start;

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

    // Walk to find the end of the tag
    for (; end < html.length; end += 1) {
        // Handle closing
        if (html[end] === '>' && quoteStack.length === 0) break;

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

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

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

    // Handle not found
    if (end === html.length) return null;

    // Done
    return { start, end };
};