Javascript Ninja

Front 1

what are functions super powers?

Back 1

Each object has a “super power” that distinguishes it from the rest; for functions it’s the ability to be invoked

Front 2

How are functions created?

Back 2

Functions are created via literals, for which a name is optional

Front 3

What happens to extra arguments in a parameter list

Back 3

Extra arguments are simply not bound to parameter names

Front 4

What happens each function invocation in terms of what is passed on the parameters?

Back 4

Each function invocation is passed two implicit parameters:
– arguments, a collection of the actual passed arguments
– this, a reference to the object serving as the function context

Front 5

What are the different ways functions can be invoked and context of each way?

Back 5

Functions can be invoked in various ways, and the invocation mechanism determines
the function context value:
– When invoked as a simple function, the context is the global object (window).
– When invoked as a method, the context is the object owning the method.
– When invoked as a constructor, the context is a newly allocated object.
– When invoked via the apply() or call() methods of the function, the context
can be whatever the heck we want.

Front 6

How can we “fool” methods into operating on objects that aren’t the object that they’re methods for?

Back 6

By controlling what function context is passed to a function invocation, we can “fool” methods into operating on objects that aren’t the object that they’re methods for. This can be useful for leveraging already existing methods on objects like Array and Math to operate on our own data.

Front 7

What is a gotcha for javascript prototypes?

Back 7

1. Extending the Object Object prototype -> every object would have the change
2. extending the the Number object -> literals can give problems to browsers
3. arrays ie and the length property for arrays for example

Front 8

What are the two purposes a function can serve?

Back 8

as normal funcions and as constructors

Front 9

How do you get a reference to the currently executing function?

Back 9

arguments.callee

Front 10

How do you test constructors

Back 10

The instanceof operator for a constructed object tests for its constructor.

Front 11

How do you test if someone called a function as a constructor from with that function

Back 11

if (!(this instanceof arguments.callee)) {
return new User(first,last);
}

Front 12

What should a custom event system should have the ability to do?

Back 12

1. add event listeners
2. remove event listners
3. event object

Front 13

Example of Memoizing (caching) DOM elements

Back 13

function getElements(name) {
if (!getElements.cache) getElements.cache = {};
return getElements.cache[name] = getElements.cache[name] ||
document.getElementsByTagName(name);
}

Front 14

Example of Simulating array-like methods on an object

Back 14

var elems = {
length: 0,
add: function(elem){
Array.prototype.push.call(this, elem);
},
gather: function(id){
this.add(document.getElementById(id));
}
};

Front 15

Example of Generic min() and max() functions for arrays

Back 15

function smallest(array){
return Math.min.apply(Math, array);
}
function largest(array){
return Math.max.apply(Math, array);
}

Front 16

Example of using timers to break up long running tasks using a central Timer

Back 16

var timers = {
timerID: 0,
timers: [],
add: function(fn) {
this.timers.push(fn);
},
start: function() {
if (this.timerID) return;
(function runNext() {
if (timers.timers.length > 0) {
for (var i = 0; i < timers.timers.length; i++) {
if (timers.timers[i]() === false) {
timers.timers.splice(i,1);
i--;
}
}
timers.timerID = setTimeout(runNext, 0);
}
})();
},
stop: function() {
clearTimeout(this.timerID);
this.timerID = 0;
}
};