JavaScript for PHP Devs: The Good Parts (40

JavaScript for PHP
developers
The Good Parts

Karsten Dambekalns <karsten@typo3.org>

Freitag, 15. Mai 2009

What this is about
the JavaScript language

not DOM
not browsers
not JS frameworks
not website building


Am I qualiﬁed?

Probably not, when it comes to JS
Absolutely when it comes to PHP


My JS background
First JS usage in the days of NN4
Used DynAPI, modiﬁed it
Saw alert() ﬁx timing issues in browsers
Was happy when I did not have to use
JavaScript anymore
Thought I would never touch it again


In JavaScript, there is
a beautiful, elegant,
highly expressive
language...


...that is buried under
a steaming pile of
good intentions and
blunders.
Douglas Crockford


Grammar


Names
Names can be chosen freely
Some words are reserved, most of them not
used in JavaScript, though
Some word should have been reserved:
NaN, Inﬁnity, undeﬁned


Numbers

Only one type, 64 bit ﬂoating point internally
Numbers have methods

(Most things in JavaScript are objects)


Strings
16 bit Unicode, as such somewhat limited
Strings have methods and properties
toUpperCase(), length
Concatenation is done with +, as is addition

(Beware of errors as a result of this!)


var
Most confusing for me was var – it seemed to
make no difference most of the time
Inside a function var deﬁnes a function’s
private variables
Otherwise variables will be globally accessible!


Type issues
typeof returns a string with a type
For arrays and null it returns ‘object’
typeof NaN === ‘number’ // true!
undeﬁned and NaN are global variables – you
can change their values


Functions


Basics

Functions are objects, they can be
stored in variables, arrays, objects
passed as arguments and returned
Functions can have methods (they are objects!)


Deﬁning functions
JavaScript has a function statement and a
function expression:
function foo() {}
means about the same as
var foo = function foo() {}
Remember: functions are values


Closure
Inner functions can access parameters and
variables of the context in which they are
created
This can be used
to protect variables against manipulation
to keep values over function calls


var myObject = function () {
var value = 0;
return {
increment: function (inc) {
value += typeof inc === ‘number ? inc : 1;
}
getValue: function () {
return value;
}
}();


Objects


Basics
Numbers, strings, booleans, null, undeﬁned are
simple types
Everything else is an object: arrays, functions,
regular expressions
Objects have properties with name and value
Objects are class free


Object literals
Very cool way of creating objects, confusing if
seen for the ﬁrst time (no new?!)
var ﬂight = {
airline: ‘FLOW Flights’,
number: 3,
captain: { ... }
}


The new statement
new creates an object that inherits from the
operand, then calls the operand with the
created object bound to this
If the operand customizes the object but you
forgot new, you change global variables!
If you use new, make constructor method
names UpperCamelCase


Inheritance
Objects inherit from objects, no classes
Prototypal inheritence allows to augment
existing objects during runtime:
Foo.prototype.bar = function () { ... }
Even built-in objects can be enhanced
Local properties hide inherited ones


Arrays


Basics
Arrays can be created with array literals:
var data = [‘one’, ‘two’, ‘three’];
The length property of an array
is the largest integer property name +1
can be set and thus cut off arrays at the end


Array or Object?
Simple rule for what to use:
When property names are small sequential
integers, use an array. Otherwise an object.
Hard to ﬁnd out what you have:
You need to deﬁne a useful is_array method
yourself.


Awful & bad parts


Semicolon inerstion
JavaScript tries to ﬁx programs by inserting
semicolons – do not rely on that!
What does this return?
return
{
status: true
};


parseInt

parseInt(’16’) == parseInt(’16 tons’) == 16
parseInt(’08’) returns 0 because it assumes
octal numbers
Always provide the radix parameter to parseInt


Bitwise operators

Avoid them if you think you gain speed
All numbers are ﬂoating point, so bitwise
operators convert to integer and back


Read this!
JavaScript: The Good Parts
Douglas Crockford
O’Reilly


Thanks!


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