Ch11 OneTask At A Time

1.Extracting Values from an Object

 

var old = function () {

 

    var place = location_info["LocalityName"]; // e.g. "Santa Monica"

    if (!place) {
        place = location_info["SubAdministrativeAreaName"]; // e.g. "Los Angeles"
    }
    if (!place) {
        place = location_info["AdministrativeAreaName"]; // e.g. "California"
    }
    if (!place) {
        place = "Middle-of-Nowhere";
    }
    if (location_info["CountryName"]) {
        place += ", " + location_info["CountryName"]; // e.g. "USA"
    } else {
        place += ", Planet Earth";
    }
    return place;
}

 

//we rewrote the original code to solve each of these tasks independently.

 

var town = location_info["LocalityName"]; // e.g. "Santa Monica"
var city = location_info["SubAdministrativeAreaName"]; // e.g. "Los Angeles"
var state = location_info["AdministrativeAreaName"]; // e.g. "CA"
var country = location_info["CountryName"]; // e.g. "USA"

 

// Start with the default, and keep overwriting with the most specific value.

var RefactoredCode = function () {

    var second_half = "Planet Earth";
    if (country) {
        second_half = country;
    }
    if (state && country === "USA") {
        second_half = state;
    }

    var first_half = "Middle-of-Nowhere";
    if (state && country !== "USA") {
        first_half = state;
    }
    if (city) {
        first_half = city;
    }
    if (town) {
        first_half = town;
    }

    return first_half + ", " + second_half;
}

var RefactoredCode2 = function () {

    var second_half = "Planet Earth";
    if (country) {
        second_half = country;
    }
    if (state && country === "USA") {
        second_half = state;
    }

    var first_half = "Middle-of-Nowhere";
    if (state && country !== "USA") {
        first_half = state;
    }
    if (city) {
        first_half = city;
    }
    if (town) {
        first_half = town;
    }

    return first_half + ", " + second_half;
}

 

2. Tasks Can Be Small

/*
When the user clicks one of the buttons (to make/change her vote), the following JavaScript
is called:
    vote_changed(old_vote, new_vote); // each vote is "Up", "Down", or ""
This function updates the total score and works for all combinations of old_vote/new_vote:*/

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);
};

 

/*
We can make the code easier to read by solving each task separately. The following code solves
the first task, of parsing the vote into a numerical value:*/

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

//Now the rest of the code can solve the second task, updating score:
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);
}
/*As you can see, this version of the code takes a lot less mental effort to convince yourself that
it works. That’s a big part of what makes code “easy to understand.”*/