《编写可读代码的艺术》第11章 一次只做一件事

    应该把代码组织得一次只做一件事，任务可以很小

vote_changed(old_vote, new_vote); // each vote is "Up", "Down", or ""

var vote_changed = function (old_vote, new_vote) {
    var score = get_score();
    if (new_vote !== old_vote) {
        if (new_vote === 'Up') {
            score += (old_vote === 'Down' ? 2 : 1);
        } else if (new_vote === 'Down') {
            score -= (old_vote === 'Up' ? 2 : 1);
        } else if (new_vote === '') {
            score += (old_vote === 'Up' ? -1 : 1);
        }
    }
    set_score(score);
}; 

//上面的代码有一些错综复杂的细节，看上去只做了一件事，实际上做了两件事情。
// 1. 把old_vote 和 new_vote解析成数字
// 2. 更新分数

var vote_value = function (vote) {
    if (vote === 'Up') {
        return +1;
    }
    if (vote === 'Down') {
        return -1;
    }
    return 0;
};

var vote_changed = function (old_vote, new_vote) {
    var score = get_score();
    score -= vote_value(old_vote); // remove the old vote
    score += vote_value(new_vote); // add the new vote
    set_score(score);
};