JavaScript @ CTK

JavaScript
Java is to JavaScript as ham is to hamster

• The basic language
• The good parts
• The bad parts
• The salvation

The basic language
Do what I mean

function fib(n) {
if (n == 1 || n == 2) {
return 1;
}
return fib(n-1) + fib(n-2);
}
alert(fib(100));

var burt = new Person();
burt.age = 2;
burt.father = ”Gustav”;

try {
var input = prompt();
if (input <= 0) {
throw ”Natural plz”;
}
alert(fib(input));
} catch (ex) {
alert(”Doh: ” + ex);
}

var s1 = ”a ‘quoted’ string”;
var s2 = ’a ”quoted” string’;
var s3 = ”a ‘quoted” string”;

var a1 = [2, 3, 5, 7, 11];
var a2 = [”foo”, ”bar”];
var a3 = [2, ”foo”, null];

var p = /^[A-Z][a-z]*$/;
alert(”Jakob”.match(p));
alert(”iPhone”.match(p));

The good parts
First-class functions, object literals, closures, prototyping
and dynamic arguments

var burt = new Person();
burt.age = 2;
burt.father = ”Gustav”;
burt.tellAge = function() {
alert(”Age: ” + this.age);
}
burt.tellAge();
burt.age = 3;
burt.tellAge();

var p = [2, 3, 5, 7, 11];
alert(p.filter(function(x) {
return x & 1 == 0;
}));

get(”jsonip.com”, function(x) {
alert(x);
});

var burt = {
age: 2,
father: ”Gustav”,
tellAge: function() {
alert(”Age: ” + this.age);
},
employees: [”Jakob”, ... ]
}
var whichOne = prompt();
alert(burt[whichOne]);

for (var property in burt) {
alert(property);
alert(burt[property]);
}

burt.lookMom = ”a new value!”;
alert(Object.keys(burt));
alert(Object.values(burt));

var json = {
”xml”: ”no”,
”json”: true,
”numbers”: [1, 2, 3],
”functions”: false,
”recursive”: {
”guess”: ”Hell yeah!”
}
}

class Counter {
private int x = 0;
public void count() {
return x++;
}
}
var c1 = new Counter();
var c2 = new Counter();
var a = [c1.count(),
c1.count(),
c2.count()];
alert(a);

function counter() {
var x = 0;
var f = function() {
return x++;
}
return f;
}
var c1 = counter();
var c2 = counter();
var a = [c1(), c1(), c2()];
alert(a);

• C lets us forget stacks, heaps and jumps
• Java lets us forget memory management
• JavaScript lets us forget creating state

function Animal(name) {
this.name = name;
this.talk = function() {
alert(this.name + ”: huh?”);
}
}
var a = new Animal(”garfield”);
var b = new Animal(”lassie”);
alert(a.name);
alert(b.talk());

function Animal(name) {
this.name = name;
}
Animal.prototype.talk = f() {
alert(this.name + ”: huh?”);
}
var a = new Animal(”garfield”);
var b = new Animal(”lassie”);
alert(a.name);
alert(b.talk());

function clone(o) {
function F() {}
F.prototype = o;
return new F();
}

The bad parts
The bad and the ugly

var sum = eval(”1 + 4”);
eval(”var x = 10”);
eval(”alert(x + sum)”);

• Opens up the code for injection attacks
• Debugging becomes hell
• Slow execution

if (x) {
alert(”when?”);
}

• Not null
• Not undeﬁned
• Not false
• Not 0
• Not the empty string

// Style #1
function foobar() {
x = 10;
}
// Style #2
function foobar() {
var x = 10;
}
// Style #3
var x;
function foobar() {
x = 10;
}

fs.readFileSync(
sourceDir + "/" + files[i],
encoding = "utf8"
);

function foobar() {
var x = 1 + 2
return x
}

function foobar() {
var x = 1 + 2;
return
x;
}

with(burt) {
alert(age);
alert(father);
}

with(burt) {
age = 3;
foo = ”bar”;
}

var a = parseInt(”123”);
var b = parseInt(”110”, 2);
var c = parseInt(”0123”);

Everything is an object
(except when parsing numbers)

alert(x.toString());
alert(1.toString());

The salvation
Good coding practices, common sense & static analysis

JavaScript @ CTK

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Editor's Notes