可以加一个逻辑，比如如果startPermlink是post的permlink，就忽略。

function getPosts(author, startPermlink = null, limit = 100, posts = []) {
    return new Promise((resolve, reject) => {
        let beforeDate = new Date().toISOString().split('.')[0];
        steem.api.getDiscussionsByAuthorBeforeDate(author, startPermlink, beforeDate, limit, function (err, result) {
            if (result.length > 1) {
                let newResult = [];
                result.forEach(post =>{
                    if(post.permlink!=startPermlink){
                        newResult.push(post);
                    }
                });
                posts = [...posts, ...newResult];
                getPosts(author, result[result.length - 1].permlink, limit, posts)
                .then(resolve)
                .catch(reject);
            } else {
                resolve(posts);
            }
        });
    });
}