// Some testing.

function Vector(x, y) {

this.x = x;

this.y = y;

}

Vector.prototype.plus = function(other) {

return new Vector(this.x + other.x, this.y + other.y);

}

function testVector() {

var p1 = new Vector(10, 20);

var p2 = new Vector(-10, 5);

var p3 = p1.plus(p2);

if (p1.x !== 10) return "fail: p1.x property";

if (p1.y !== 20) return "fail: p1.y property";

if (p2.x !== -10) return "fail: p2.x property";

if (p2.y !== 5) return "fail: p2.y property";

if (p3.x !== 0) return "fail: p3.x property from plus";

if (p3.y !== 25) return "fail: p3.y property from plus";

return "everything okay";

}

console.log(testVector());

// Assertion

function AssertionFailed(message) {

this.message = message;

}

AssertionFailed.prototype = Object.create(Error.prototype);

function assert(test, message) {

if (!test) {

throw new AssertionFailed(message);

}

}

function lastElement(array) {

assert(array.length > 0, "empty array in lastElement");

return array[array.length - 1];

}

console.log(lastElement([1, 2, 3, 4, 5,]));

console.log(lastElement([""]));

var box = {

locked: true,

unlock: function() { this.locked = false; },

lock: function() { this.locked = true; },

_content: [],

get content() {

if (this.locked) throw new Error("Locked!");

return this._content;

}

};

function withBoxUnlocked(body) {

var locked = box.locked;

if (!locked)

return body();

box.unlock();

try {

return body();

} finally {

box.lock();

}

}

withBoxUnlocked(function() {

box.content.push("gold piece");

});

try {

withBoxUnlocked(function() {

throw new Error("Pirates on the horizon! Abort!");

});

} catch (e) {

console.log("Error raised:", e);

}

console.log(box.locked);