facebook-event-scraper-fetch/dist/utils/json.js

A slim module for scraping Facebook event data in milliseconds.

"use strict";
// TODO: make this into its own library. Couple things to add before releasing to public
// - Add a new method for getting keys with direct values (essentially use " as the start and end character)
// - Handle json with whitespaces
// - Use a separate func for arrays (eg findJsonArrayInString)
Object.defineProperty(exports, "__esModule", { value: true });
exports.findJsonInString = void 0;
// TODO: Use better typing, eg:
// interface ReturnData {
//   startIndex: number;
//   endIndex: number;
//   jsonData: Record<string, any> | Record<string, any>[] | null;
// }
const findJsonInString = (dataString, key, isDesiredValue) => {
    const prefix = `"${key}":`;
    let startPosition = 0;
    // This loop is used for iterating over found json objects, and checking if they are the one we want using the isDesiredValue callback
    while (true) {
        let idx = dataString.indexOf(prefix, startPosition);
        if (idx === -1) {
            return { startIndex: -1, endIndex: -1, jsonData: null };
        }
        idx += prefix.length;
        const startIndex = idx;
        const startCharacter = dataString[startIndex];
        // Value is null
        if (startCharacter === 'n' &&
            dataString.slice(startIndex, startIndex + 4) === 'null') {
            return { startIndex, endIndex: startIndex + 3, jsonData: null };
        }
        // Unexpected start character
        if (startCharacter !== '{' && startCharacter !== '[') {
            throw new Error(`Invalid start character: ${startCharacter}`);
        }
        const endCharacter = startCharacter === '{' ? '}' : ']';
        let nestedLevel = 0;
        // This is set to true anytime idx is pointing to a string value. In these cases, we want to ignore any start or end characters we find
        let isIndexInString = false;
        // This loop iterates over each character in the json object until we get to the end of the object
        while (idx < dataString.length - 1) {
            // In the first iteration, idx is pointing to the first "{" or "[", so we start by incrementing it
            idx++;
            // Note that '\\' actually refers to a single quote, but we need to escape the backslash since Node will otherwise interpret it as an escape character
            if (dataString[idx] === '"' && dataString[idx - 1] !== '\\') {
                isIndexInString = !isIndexInString;
            }
            else if (dataString[idx] === endCharacter && !isIndexInString) {
                if (nestedLevel === 0) {
                    break;
                }
                nestedLevel--;
            }
            else if (dataString[idx] === startCharacter && !isIndexInString) {
                nestedLevel++;
            }
        }
        const jsonDataString = dataString.slice(startIndex, idx + 1);
        // TODO: See how useful error message is from this. If not good enough, add handling & rethrowing
        const jsonData = JSON.parse(jsonDataString);
        if (!isDesiredValue || isDesiredValue(jsonData)) {
            return { startIndex, endIndex: idx, jsonData };
        }
        startPosition = idx;
    }
};
exports.findJsonInString = findJsonInString;