note for "The Art of Readable Code" - CH10 Extracting Unrelated Subproblems

將子問題抽離，讓function專注在處理問題本身上面，首先要先了解這個function的"目的"，接著抽離與"目的"無關的子問題，將這些子問題一一寫成獨立的function，如:（簡單說就主程式專注在邏輯上，細節部分就一一寫成sub function處理）

// Return which element of 'array' is closest to the given latitude/longitude.
// Models the Earth as a perfect sphere.
var findClosestLocation = function (lat, lng, array) {
    var closest;
    var closest_dist = Number.MAX_VALUE;
    for (var i = 0; i < array.length; i += 1) {
        // Convert both points to radians.
        var lat_rad = radians(lat);
        var lng_rad = radians(lng);
        var lat2_rad = radians(array[i].latitude);
        var lng2_rad = radians(array[i].longitude);
        // Use the "Spherical Law of Cosines" formula.
        var dist = Math.acos(Math.sin(lat_rad) * Math.sin(lat2_rad) +
                             Math.cos(lat_rad) * Math.cos(lat2_rad) *
                             Math.cos(lng2_rad - lng_rad));
        if (dist < closest_dist) {
             closest = array[i];
             closest_dist = dist;
        }
    }
    return closest;
};

抽離後的code
var spherical_distance = function (lat1, lng1, lat2, lng2) {
    var lat1_rad = radians(lat1);
    var lng1_rad = radians(lng1);
    var lat2_rad = radians(lat2);
    var lng2_rad = radians(lng2);
    // Use the "Spherical Law of Cosines" formula.
    return Math.acos(Math.sin(lat1_rad) * Math.sin(lat2_rad) +
                     Math.cos(lat1_rad) * Math.cos(lat2_rad) *
};

var findClosestLocation = function (lat, lng, array) {
    var closest;
    var closest_dist = Number.MAX_VALUE;
    for (var i = 0; i < array.length; i += 1) {
        var dist = spherical_distance(lat, lng, array[i].latitude, array[i].longitude);
        if (dist < closest_dist) {
            closest = array[i];
            closest_dist = dist;
        }
    }
    return closest;
};

抽離這些子問題的另一個好處容易優化，比如有更好的方式去運算spherical_distance()或是變更findClosestLocation()的運算邏輯。建立通用的function也是一個很好也很重要的習慣，當你開發一個新的program時，就可以運用這些通用function，快速建立一個prototype。

Simplifying an Existing Interface & Reshaping an Interface to Your Needs

如果既有的API不好用，那就包裝他或改寫他吧，我在A Wrap for service/thread也包裝了一些API，讓自己易於開發，有必要也會進行Reshaping/Re-factor等等步驟。

參考資料:
• The Art of Readable Code