Arrays.md

#Array

Arrays are really just a type of object that is optimized to bind values to successive numeric integer keys. Calling typeof on an array reveals it to be just an object. It has built in property functions that perform operations/actions on its elements. These operations do not perform in place modification of the array (the elements in the array are never changed) but rather they return a new array or object with the desired changes affected to its elements.

Array Methods

####push

array.push( item );

Adds an element item to the end of the array. Does not return any value.

####pop

array.pop()

Removes an element from the end of the array and returns it.

####join

array.join( delimiter )

Joins an array into a string using the value of delimiter (given as a string) as the elements placed between each of the elements as they are placed in the string.

####forEach

array.forEach( action )

Applies an action to each element of the array. The action is a function that is passed every element of the array one argument at a time by the forEach method. action is of the form:

function( item ) {
	...
}

####filter

array.filter( predicate )

Applies predicate to each element of the array and returns an array populated by only the elements that return true when passed as arguments to the predicate. predicate takes only a single argument, returns a boolean value and is of the form:

function( item ) {
	...
	return boolean;
}

####map

 array.map( action )

Maps each element of the array to a new element based on the action passed. Returns a new array with each of the elements in the original array mapped according to action. The return value of the action function is the item that will be added to the array returned by map. The returned mapped array and the original array will have the same length. action is of the form:

function( item ) {
	...
	return newItem;
}

####reduce

array.reduce( operation )

Reduces an array to a single value by using operation. The operation is called once for every element of the array. operation is of the form:

function( lastReturnValue, currentArrayValue ) {
	...
	return newReturnValue;
}

Two arguments are passed to operation. The first argument lastReturnValue is the value that was returned from the last run of operation and the second argument currentArrayValue is the next value of the array being passed to operation. Reduce is very useful for things like summing all of the values of an array or combining them into a aggregate value.