Dictionaries Back

A dictionary is a data structure that stores data as key-value pairs. In JavaScript, the Object class is designed to operate as a dictionary. In this chapter, we'll use the features of the Object class to build a Dictionary class.

The Dictionary Class

The basic for the Dictionary class is the Array class rather than the Object class, because we also want to sort the keys of a dictionary, which Object can not support.

function Dictionary() {
    this.dataStore = [];
    this.add = add;
    this.find = find;
    this.remove = remove;
    this.showAll = showAll;
}

function add(key, value) {
    this.dataStore[key] = value;
}

function find(key) {
    return this.dataStore[key];
}

function remove(key) {
    delete this.dataStore[key];
}

function showAll() {
    var dataStore = this.dataStore;

    for (var i in dataStore) {
        console.log(i + ' -> ' + dataStore[i]);
    }
}

Auxiliary (輔助性) Functions for the Dictionary Class

function count() {
    var n = 0;

    for (var i in this.dataStore) {
        n++;
    }

    /**
     * in this case, you can not use this.dataStore.length
     * as the returned result.
     */
    return n;
}

function clear() {
    var dataStore = this.dataStore;

    for (var i in dataStore) {
        delete dataStore[i];
    }
}

Adding Sorting to the Dictionary Class

Even if there is a method to sort for any Array object, it only works well with integer indexes but not string keys. Therefore, we can use another method Object.keys() function to solve this problem, which should return an object which has provied the sorting method sort():

function showAll() {
    var dataStore = this.dataStore;

    for (var i in Object.keys(dataStore).sort()) {
        console.log(i + ' -> ' + dataStore[i]);
    }
}

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