javascript - observer 范例

function observable (value, condition, callback){
    this.value = value;
    this.condition = condition;
    this.callback = callback;
}

observable.prototype = {
    get value () {
        return this._value;
    },
    set value (value) {
        this._value = value;
        if (this.condition && this.callback && this.condition (value)) {
            this.callback (value);
        }
    }
};

condition = function (value) {
    console.log ('condition', value);
    return value === 2;
}

callback = function (value) {
    console.info ('Big Brother is watching you!');
}

var a = new observable (0, condition, callback);

console.log ('set value to 1');
a.value = 1;
console.log ('set value to 2');
a.value = 2;
console.log ('set value to 3');
a.value = 3;