This what I have learned so far.

• Four essential data types in JavaScript include strings, numbers, booleans, and null.

console.log('JavaScript'); // String - can bet with single quotes ('Hello') or double quotes ("World!").
console.log(33.7); // Numbers - Any number, including numbers with decimals: 4, 1516, .002, 23.42. In the example above, 40.7 is a number.
console.log(true); // Booleans Either true or false, with no quotations. In the example above, true is a boolean.
console.log(null); // Null Can only be null. It represents the absence of value.

• Data is printed, or logged, to the console with command console.log().

console.log("Pineaplle");
console.log("MATRIX");

Gets you an output:

Pineaplle
MATRIX

• Four built-in mathematical operators include +, -, *, and /.

Using these you can perform various mathematical operations:

console.log(32 + 3.5);
console.log(2017 - 1969);
console.log(65 / 240);
console.log(0.2708 * 100)

Output:

35.5
48
0.2708333333333333
27.08

• JavaScript associates certain properties with different data types.

Using those properties you can find out the length of the text you get:

console.log('Teaching the world how to code'.length)

Output:

30

• JavaScript has built-in methods for different data types.

You can perform various different actions with built-in methods. You can find a list of built-in string methods in the JavaScript documentation. Developers use documentation as a reference tool. It describes JavaScript’s keywords, methods, and syntax.

// Log Codecademy in all uppercase letters
console.log('Codecademy'); 
console.log('Codecademy'.toUpperCase())

console.log('Hey'.startsWith('H'))

// Use a string method to log the following statment without whitespace at the beginning and end of it.
console.log('    Remove whitespace   '.trim());

Output:

Codecademy
CODECADEMY
true
Remove whitespace

• Libraries are collections of methods that can be called without an instance.

You can find all the different Math methods in the JavaScript math library.

When you want to call a method without an instance. You can use JavaScript libraries for this. Libraries contain methods that you can call without creating an instance.

One collection contains mathematical methods, aptly named the Math library which have these examples below.

And also there are way more then mentioned previously. For example Built In Number library.

console.log(Math.floor(Math.random() * 100 )); //random number rounded to decimal

console.log(Math.ceil(43.8));

console.log(Number.isInteger(2017));

Output:

78
44
true

• You can write single-line comments with // and multi-line comments between /*and */.

There are only two types of comments. But you can use them to perform all the tasks.

//Opening line
console.log('It was love at first sight.');

/*console.log('The first time Yossarian saw the chaplain he fell madly in love with him.');
console.log('Yossarian was in the hospital with a pain in his liver that fell just short of being jaundice.');
/*console.log('The doctors were puzzled by the fact that it wasn\'t quite jaundice.');
console.log('If it became jaundice they could treat it.');
console.log('If it didn\'t become jaundice and went away they could discharge him.');
console.log('But this just being short of jaundice all the time confused them.');*/

Output: