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Subtypes must be substitutable for their base types.
派生类型必须可以替换它的基类型。
function Vehicle(my) {
var my = my || {};
my.speed = 0;
my.running = false;
this.speed = function() {
return my.speed;
};
this.start = function() {
my.running = true;
};
this.stop = function() {
my.running = false;
};
this.accelerate = function() {
my.speed++;
};
this.decelerate = function() {
my.speed--;
}, this.state = function() {
if (!my.running) {
return "parked";
}
else if (my.running && my.speed) {
return "moving";
}
else if (my.running) {
return "idle";
}
};
}
function FastVehicle(my) {
var my = my || {};
var that = new Vehicle(my);
that.accelerate = function() {
my.speed += 3;
};
return that;
}
var maneuver = function(vehicle) {
write(vehicle.state());
vehicle.start();
write(vehicle.state());
vehicle.accelerate();
write(vehicle.state());
write(vehicle.speed());
vehicle.decelerate();
write(vehicle.speed());
if (vehicle.state() != "idle") {
throw "The vehicle is still moving!";
}
vehicle.stop();
write(vehicle.state());
};
Favor object composition over class inheritance
尽量使用对象组合而不是类继承
var rectangle = {
length: 0,
width: 0
};
var square = {};
(function() {
var length = 0, width = 0;
// 注意defineProperty方式是262-5版的新特性
Object.defineProperty(square, "length", {
get: function() { return length; },
set: function(value) { length = width = value; }
});
Object.defineProperty(square, "width", {
get: function() { return width; },
set: function(value) { length = width = value; }
});
})();
var g = function(rectangle) {
rectangle.length = 3;
rectangle.width = 4;
write(rectangle.length);
write(rectangle.width);
write(rectangle.length * rectangle.width);
};