JS Data Structures.md

JavaScript Data Structures

Besides numbers, strings, booleans, the non-values, and functions, there are two additional native JavaScript types.

Arrays

Arrays are indexed collections of variables, all stored inside a single variable. Arrays are bounded by [ and ], and individual values inside of arrays are comma-delimited.

var numbers = [1, 2, 3, 4]

The values inside of an array can be of any type (including arrays).

var randomStuff = [
  "string", 
  42, 
  true, 
  function() { return "hello, world!" },
  ["a", "b", "c"]  
];

In JavaScript, arrays are zero-indexed -- meaning the first element is at index 0, the second is at index 1...

To access a specific value from within an array:

// using randomStuff array above

console.log(randomStuff[0]); // "string"
console.log(randomStuff[1]); // 42
console.log(randomStuff[3]()); // "hello, world!"
console.log(randomStuff[4][2]); // "c"

// Array values can be changed
randomStuff[2] = false;

console.log(randomStuff); // entire contents of array

Every array has a built in property - length.

Some built-in functions that can be performed on any array:

• push - adds value to right
• pop - remove value from right, returns that value
• unshift - adds value to left
• shift - remove value from left, returns that value
• reverse - reverses array members

var testArray = [ "a", "b", "c" ];

console.log(testArray.length); // 3

testArray.push("d");
console.log(testArray); // [ "a", "b", "c", "d" ]

console.log(testArray.pop()); // "d"
console.log(testArray); // [ "a", "b", "c" ]

console.log(testArray.shift()); // "a"
console.log(testArray); // [ "b", "c" ]

testArray.unshift("e");
console.log(testArray); // [ "e", "b", "c" ]

testArray.reverse();
console.log(testArray); // [ "c", "b", "e" ]

// Use a loop to iterate over the items in an array
for (var x = 0; x < testArray.length; x++) {
    console.log(testArray[x]);
}

/* Prints:
"c"
"b"
"e"
*/

Objects

Objects are named collections of variables, all stored inside a single variable. Objects are bounded by { and }. Individual values inside of objects are comma-delimited, and given distinct names within the object; the names must be strings or numbers, and definition occurs with :.

var myObject = {
    someProperty: "someValue",
    someOtherProperty: [1, 2, 3]
};

JavaScript objects are mutable, which means that after being created, properties can be added, removed, and edited at will. To interact with an object:

var testObject = {
    first: "hello",
    second: "world"
};

// Dot notation works fine
console.log(testObject.first); // "hello"

// So does bracket notation
console.log(testObject["second"]); // "world"

// Properties can be changed
testObject.first = "hola";
testObject["second"] = "mundial";

// Properties can be added
testObject.third = "muchachos";

// Use a loop to iterate over the properties in an object
// Note different syntax

for (var x in testObject) {
    console.log(x + " : " + testObject[x]);
}
/* Prints (in unpredictable order):
"first : hola"
"second : mundial"
"third : muchachos"
*/

Like with arrays, object properties can be any types of values, including arrays and other objects.

Comprehension

Arrays and objects, while acting similar, serve different purposes.

Arrays:

• are for containing lists of items
• do not have named properties
• maintain order

Object:

• are for containing collections of disparate information
• have named properties
• do not maintain order