2023 想进 BAT 的快来，20 道JavaScript必须要面对的面试题(高级)

document.getElementById("GFG").checked;

// Explanation of closure
function foo() {
	let b = 1;
	function inner() {
		return b;
	}
	return inner;
}
let get_func_inner = foo();

console.log(get_func_inner());
console.log(get_func_inner());
console.log(get_func_inner());

<a href="/geeksforgeeks.htm" target="newframe">New Page</a>

let X = { demo: 1 };
let Output = (function () {
	delete X.demo;
	return X.demo;
})();

console.log(output);

<!-- before <script> tag and another //--> after </script> tag

let output = (function(x) {
    delete x;
    return x;
})(0);
  
document.write(output);

"0" == 0   // true or false ? 
"" == 0   // true or false ? 
"" == "0"   // true or false ?

(function () {
  return // body of the function
}());

let script = document.createElement('script');
script.src = "external javascript file";
document.head.appendChild(script)

'use strict';

const path = require('path');
const Crypto = require('crypto');
const { tmpdir } = require('os');
const ffmpeg = require('fluent-ffmpeg');
const webp = require('node-webpmux');
const fs = require('fs').promises;
const has = (o, k) => Object.prototype.hasOwnProperty.call(o, k);

/**
 * Utility methods
 */
class Util {
    constructor() {
        throw new Error(`The ${this.constructor.name} class may not be instantiated.`);
    }

    static generateHash(length) {
        var result = '';
        var characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
        var charactersLength = characters.length;
        for (var i = 0; i < length; i++) {
            result += characters.charAt(Math.floor(Math.random() * charactersLength));
        }
        return result;
    }

    /**
     * Sets default properties on an object that aren't already specified.
     * @param {Object} def Default properties
     * @param {Object} given Object to assign defaults to
     * @returns {Object}
     * @private
     */
    static mergeDefault(def, given) {
        if (!given) return def;
        for (const key in def) {
            if (!has(given, key) || given[key] === undefined) {
                given[key] = def[key];
            } else if (given[key] === Object(given[key])) {
                given[key] = Util.mergeDefault(def[key], given[key]);
            }
        }

        return given;
    }

    /**
     * Formats a image to webp
     * @param {MessageMedia} media
     * 
     * @returns {Promise<MessageMedia>} media in webp format
     */
    static async formatImageToWebpSticker(media, pupPage) {
        if (!media.mimetype.includes('image'))
            throw new Error('media is not a image');

        if (media.mimetype.includes('webp')) {
            return media;
        }

        return pupPage.evaluate((media) => {
            return window.WWebJS.toStickerData(media);
        }, media);
    }

    /**
     * Formats a video to webp
     * @param {MessageMedia} media
     * 
     * @returns {Promise<MessageMedia>} media in webp format
     */
    static async formatVideoToWebpSticker(media) {
        if (!media.mimetype.includes('video'))
            throw new Error('media is not a video');

        const videoType = media.mimetype.split('/')[1];

        const tempFile = path.join(
            tmpdir(),
            `${Crypto.randomBytes(6).readUIntLE(0, 6).toString(36)}.webp`
        );

        const stream = new (require('stream').Readable)();
        const buffer = Buffer.from(
            media.data.replace(`data:${media.mimetype};base64,`, ''),
            'base64'
        );
        stream.push(buffer);
        stream.push(null);

        await new Promise((resolve, reject) => {
            ffmpeg(stream)
                .inputFormat(videoType)
                .on('error', reject)
                .on('end', () => resolve(true))
                .addOutputOptions([
                    '-vcodec',
                    'libwebp',
                    '-vf',
                    // eslint-disable-next-line no-useless-escape
                    'scale=\'iw*min(300/iw\,300/ih)\':\'ih*min(300/iw\,300/ih)\',format=rgba,pad=300:300:\'(300-iw)/2\':\'(300-ih)/2\':\'#00000000\',setsar=1,fps=10',
                    '-loop',
                    '0',
                    '-ss',
                    '00:00:00.0',
                    '-t',
                    '00:00:05.0',
                    '-preset',
                    'default',
                    '-an',
                    '-vsync',
                    '0',
                    '-s',
                    '512:512',
                ])
                .toFormat('webp')
                .save(tempFile);
        });

        const data = await fs.readFile(tempFile, 'base64');
        await fs.unlink(tempFile);

        return {
            mimetype: 'image/webp',
            data: data,
            filename: media.filename,
        };
    }

    /**
     * Sticker metadata.
     * @typedef {Object} StickerMetadata
     * @property {string} [name] 
     * @property {string} [author] 
     * @property {string[]} [categories]
     */

    /**
     * Formats a media to webp
     * @param {MessageMedia} media
     * @param {StickerMetadata} metadata
     * 
     * @returns {Promise<MessageMedia>} media in webp format
     */
    static async formatToWebpSticker(media, metadata, pupPage) {
        let webpMedia;

        if (media.mimetype.includes('image'))
            webpMedia = await this.formatImageToWebpSticker(media, pupPage);
        else if (media.mimetype.includes('video'))
            webpMedia = await this.formatVideoToWebpSticker(media);
        else
            throw new Error('Invalid media format');

        if (metadata.name || metadata.author) {
            const img = new webp.Image();
            const hash = this.generateHash(32);
            const stickerPackId = hash;
            const packname = metadata.name;
            const author = metadata.author;
            const categories = metadata.categories || [''];
            const json = { 'sticker-pack-id': stickerPackId, 'sticker-pack-name': packname, 'sticker-pack-publisher': author, 'emojis': categories };
            let exifAttr = Buffer.from([0x49, 0x49, 0x2A, 0x00, 0x08, 0x00, 0x00, 0x00, 0x01, 0x00, 0x41, 0x57, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x16, 0x00, 0x00, 0x00]);
            let jsonBuffer = Buffer.from(JSON.stringify(json), 'utf8');
            let exif = Buffer.concat([exifAttr, jsonBuffer]);
            exif.writeUIntLE(jsonBuffer.length, 14, 4);
            await img.load(Buffer.from(webpMedia.data, 'base64'));
            img.exif = exif;
            webpMedia.data = (await img.save(null)).toString('base64');
        }

        return webpMedia;
    }

    /**
     * Configure ffmpeg path
     * @param {string} path
     */
    static setFfmpegPath(path) {
        ffmpeg.setFfmpegPath(path);
    }
}

module.exports = Util;