Functions
function declarations
function thing(p1,p2) {
code
return value;
}
- Starts with word ‘function’
- Not separately assigned to a variable
- WILL be hoisted and declared at top
vs
function expressions
var thing = function(p1, p2) {
code
return value;
};
- Assigns function with no name (annoymous) to a named variable
- Will NOT be hoisted to top, will be defined inline
IIFE’s – immediately invoked function expressions
(function(){ }());
(function(){ })();
– key identifier is surrounding parens – ()
– invoked at actual runtime
Function Overloading
Achieved with functions by examing arguments, e.g.
function abc() {
if (arguments.length === 0) { this code; }
else {
other_code; } }
The three ways to use ‘this’ with methods in javascript functions
1 With call
some_function.call(this, "text")
A particular value for ‘this’ and specific parameters
2. With apply
some_function.apply(this, "text")
A particular value for ‘this’ and, specifically, an array for any parameters
3. With bind
some_function.bind(this, "text")
‘this’ is the value for the new function, the rest are named parameters for ‘new’
Object Properties
Common Internal Properties
Data Properties, i.e. values
All Data Properties also have two attribute methods:
or
Accessor Properties, i.e. functions
All Accessor Properties also have two attribute methods:
e.g.
var tree = {
_name: "Oak",
get name() {
console.log("here1");
return this._name;
},
set name(value) {
console.log('here2');
this._name = value;
}
};
Retrieving Property Attributes
Object.getOwnPropertyDescriptor()
Constructors and Prototypes
Constructors use ‘new’ to create a new instance of a method.
Functions should be capitalized when they are used as constructors – you will be creating new instances of them with ‘new’.
All functions have an internal prototype property
You can check for it with object.hasOwnProperty(name)
Rubyists may find its usage has some similarities to Ruby’s class level methods.
When an object (function w/new constructor) has methods that are shared by all instances use a prototype function for the Object
YourObject.prototype.yourFunctionName = function() {...}
When an object (function w/new constructor) has attribute values that are shared by all instances use a prototype attribute for the Object
YourObject.prototype.yourVariableName = value
