Accessing Nested Arrays

As we have seen in earlier examples, objects can contain both nested objects and nested arrays. Similar to accessing nested objects, Array bracket notation can be chained to access nested arrays.

Here is an example of how to access a nested array:

var ourPets = [
  {
    animalType: "cat",
    names: [
      "Meowzer",
      "Fluffy",
      "Kit-Cat"
    ]
  },
  {
    animalType: "dog",
    names: [
      "Spot",
      "Bowser",
      "Frankie"
    ]
  }
];
ourPets[0].names[1]; // "Fluffy"
ourPets[1].names[0]; // "Spot"

Retrieve the second tree from the variable myPlants using object dot and array bracket notation.

Manipulating Complex Objects

Sometimes you may want to store data in a flexible Data Structure. A JavaScript object is one way to handle flexible data. They allow for arbitrary combinations of strings, numbers, booleans, arrays, functions, and objects.

Here's an example of a complex data structure:

var ourMusic = [
  {
    "artist": "Daft Punk",
    "title": "Homework",
    "release_year": 1997,
    "formats": [
      "CD",
      "Cassette",
      "LP"
    ],
    "gold": true
  }
];
This is an array which contains one object inside. The object has various pieces of metadata about an album. It also has a nested "formats" array. If you want to add more album records, you can do this by adding records to the top level array.

Objects hold data in a property, which has a key-value format. In the example above, "artist": "Daft Punk" is a property that has a key of "artist" and a value of "Daft Punk".

JavaScript Object Notation or JSON is a related data interchange format used to store data.

{
  "artist": "Daft Punk",
  "title": "Homework",
  "release_year": 1997,
  "formats": [
    "CD",
    "Cassette",
    "LP"
  ],
  "gold": true
}
Note
You will need to place a comma after every object in the array, unless it is the last object in the array.


Add a new album to the myMusic array. Add artist and title strings, release_year number, and a formats array of strings.

Basic JavaScript: Using Objects for Lookups

Objects can be thought of as a key/value storage, like a dictionary. If you have tabular data, you can use an object to "lookup" values rather than a switch statement or an if/else chain. This is most useful when you know that your input data is limited to a certain range.

Here is an example of a simple reverse alphabet lookup:

var alpha = {
  1:"Z",
  2:"Y",
  3:"X",
  4:"W",
  ...
  24:"C",
  25:"B",
  26:"A"
};
alpha[2]; // "Y"
alpha[24]; // "C"

var value = 2;
alpha[value]; // "Y"

Convert the switch statement into an object called lookup. Use it to look up val and assign the associated string to the result variable.

Selecting from Many Options with Switch Statements

If you have many options to choose from, use a switch statement. A switch statement tests a value and can have many case statements which define various possible values. Statements are executed from the first matched case value until a break is encountered.

Here is a pseudocode example:

switch(num) {
  case value1:
    statement1;
    break;
  case value2:
    statement2;
    break;
...
  case valueN:
    statementN;
    break;
}
case values are tested with strict equality (===). The break tells JavaScript to stop executing statements. If the break is omitted, the next statement will be executed.


Write a switch statement which tests val and sets answer for the following conditions:
1 - "alpha"
2 - "beta"
3 - "gamma"
4 - "delta"

Basic JavaScript: Chaining If Else Statements

if/else statements can be chained together for complex logic. Here is pseudocode of multiple chained if / else if statements:

if (condition1) {
  statement1
} else if (condition2) {
  statement2
} else if (condition3) {
  statement3
. . .
} else {
  statementN
}

Write chained if/else if statements to fulfill the following conditions:

num < 5 - return "Tiny"
num < 10 - return "Small"
num < 15 - return "Medium"
num < 20 - return "Large"
num >= 20 - return "Huge"

Basic JavaScript: Understanding Boolean Values

Another data type is the Boolean. Booleans may only be one of two values: true or false. They are basically little on-off switches, where true is "on" and false is "off." These two states are mutually exclusive.

Note
Boolean values are never written with quotes. The strings "true" and "false" are not Boolean and have no special meaning in JavaScript.

Basic JavaScript: Stand in Line

In Computer Science a queue is an abstract Data Structure where items are kept in order. New items can be added at the back of the queueand old items are taken off from the front of the queue.

Write a function nextInLinewhich takes an array (arr) and a number (item) as arguments.

Add the number to the end of the array, then remove the first element of the array.

The nextInLinefunction should then return the element that was removed.

Basic JavaScript: Understanding Undefined Value returned from a Function

Create a function addFive without any arguments. This function adds 5 to the sum variable, but its returned value is undefined.

Basic JavaScript: Return a Value from a Function with Return

We can pass values into a function with arguments. You can use a return statement to send a value back out of a function.

Example

function plusThree(num) {

  return num + 3;

}

var answer = plusThree(5); // 8

plusThree takes an argument for num and returns a value equal to num + 3.

Create a function timesFive that accepts one argument, multiplies it by 5, and returns the new value. See the last line in the editor for an example of how you can test your timesFive function.

Basic JavaScript: Local Scope and Functions

Declare a local variable myVar inside myLocalScope. Run the tests and then follow the instructions commented out in the editor.

Hint

Refreshing the page may help if you get stuck.

Basic JavaScript: Word Blanks

We will now use our knowledge of strings to build a "Mad Libs" style word game we're calling "Word Blanks". You will create an (optionally humorous) "Fill in the Blanks" style sentence.

In a "Mad Libs" game, you are provided sentences with some missing words, like nouns, verbs, adjectives and adverbs. You then fill in the missing pieces with words of your choice in a way that the completed sentence makes sense.

Consider this sentence - "It was really ____, and we ____ ourselves ____". This sentence has three missing pieces- an adjective, a verb and an adverb, and we can add words of our choice to complete it. We can then assign the completed sentence to a variable as follows:

var sentence = "It was really" + "hot" + ", and we" + "laughed" + "ourselves" + "silly.";

In this challenge, we provide you with a noun, a verb, an adjective and an adverb. You need to form a complete sentence using words of your choice, along with the words we provide.

You will need to use the string concatenation operator + to build a new string, using the provided variables: myNoun, myAdjective, myVerb, and myAdverb. You will then assign the formed string to the result variable.

You will also need to account for spaces in your string, so that the final sentence has spaces between all the words. The result should be a complete sentence.

Basic JavaScript: Appending Variables to Strings

Just as we can build a string over multiple lines out of string literals, we can also append variables to a string using the plus equals (+=) operator.


Set someAdjective and append it to myStr using the += operator.

#100daysofcode D29 - Basic JavaScript: Concatenating Strings with Plus Operator

Basic JavaScript: Concatenating Strings with Plus Operator
In JavaScript, when the + operator is used with a String value, it is called the concatenation operator. You can build a new string out of other strings by concatenating them together.

Example

'My name is Alan,' + ' I concatenate.'
Note
Watch out for spaces. Concatenation does not add spaces between concatenated strings, so you'll need to add them yourself.


Build myStr from the strings "This is the start. " and "This is the end." using the + operator.

#100DAYSOFCODE D28 - Basic JavaScript: Escape Sequences in Strings

Quotes are not the only characters that can be escaped inside a string. There are two reasons to use escaping characters: First is to allow you to use characters you might not otherwise be able to type out, such as a backspace. Second is to allow you to represent multiple quotes in a string without JavaScript misinterpreting what you mean. We learned this in the previous challenge.

Code	Output
\'	single quote
\"	double quote
\\	backslash
\n	newline
\r	carriage return
\t	tab
\b	backspace
\f	form feed

Note that the backslash itself must be escaped in order to display as a backslash.

---

Assign the following three lines of text into the single variable myStrusing escape sequences.

FirstLine
    \SecondLine
ThirdLine

You will need to use escape sequences to insert special characters correctly. You will also need to follow the spacing as it looks above, with no spaces between escape sequences or words.

Here is the text with the escape sequences written out.

FirstLine newlinetabbackslash SecondLinenewline ThirdLine

Escaping Literal Quotes in Strings: #100days of code D27

When you are defining a string you must start and end with a single or double quote. What happens when you need a literal quote: "or 'inside of your string?

In JavaScript, you can escape a quote from considering it as an end of string quote by placing a backslash (\) in front of the quote.

var sampleStr = "Alan said, \"Peter is learning JavaScript\".";

This signals to JavaScript that the following quote is not the end of the string, but should instead appear inside the string. So if you were to print this to the console, you would get:

Alan said, "Peter is learning JavaScript".

---

Use backslashes to assign a string to the myStrvariable so that if you were to print it to the console, you would see:

I am a "double quoted" string inside "double quotes".

D26 Basic #JavaScript: Compound Assignment With Augmented Multiplication

The *=operator multiplies a variable by a number.

myVar = myVar * 5;

will multiply myVarby 5. This can be rewritten as:

myVar *= 5;

---

Convert the assignments for a, b, and cto use the *=operator.

1st #freecodcamp Certification is in the bag...

Long over due, after a few starts and long pauses. One down 5 to go.