Only practical for Discord selfbots. Use with Discord.js

spellcheck.js

let rp = require('request-promise-native');
const dns = require('dns');
const os = require('os');

function checkSpelling(client, text)    {

    return new Promise((resolve, reject) => {
        dns.lookup(os.hostname(), (err, address, family) => {
            if(err) return reject(err);
            resolve(address);
        });
    }).then(ip => {
        rp = rp.defaults({
            baseUrl: 'https://api.cognitive.microsoft.com/bing/v5.0',
            headers: {
                'Ocp-Apim-Subscription-Key': process.env.BING,
                'X-MSEdge-ClientID': client.user.id,
                'X-Search-ClientIP': ip
            },
            method: 'post'
        });

        return rp({
            uri: 'SpellCheck',
            qs: {
                mode: 'proof',
                text: text
            }
        });
    }).then(JSON.parse).then(res => {
        let corrected = text;
        let offset = 0;

        for(const correction of res.flaggedTokens)  {
            let start = correction.offset + offset;
            let end = start + correction.token.length;
            const suggestion = correction.suggestions[0].suggestion;

            offset += suggestion.length - correction.token.length;        // how much shorter or longer the string has become through replacement.

            if(suggestion.length === 0)  {
                offset--;
                start--;
            }

            corrected = corrected.substring(0, start) + suggestion + corrected.substring(end);
        }


        return corrected;
    });
}

module.exports = checkSpelling;