Every programming language has its own way of representing data.

In javascript, there are 7 data types.

## 1. Number

Numbers in JavaScript are stored as 64-bit floats, and can be manipulated using the built-in operators.

There are a few noteworthy cases for numbers:

*Largest safe integer*: The largest possible integer that can be represented with 100% accuracy is given by`Number.MAX_SAFE_INTEGER`

, and is equal to 2^{53}- 1, or`9007199254740991`

. Numbers are always signed, so`Number.MIN_SAFE_INTEGER`

gives the minimum safe integer, which is`-1`

times max safe integer.*Largest value*: The largest possible value than can be stored is given by`Number.MAX_VALUE`

, and is equal to 2^{1024}- 1. Again, the minimum value is`-1`

times the maximum value.*Smallest value*: The smallest value greater than 0 is given by`Number.MIN_VALUE`

, and is equal to 2^{-1074}, or`5e-324`

.*Epsilon*: The difference between 1 and the least number greater than 1 is given by`Number.EPSILON`

, and is 2^{-52}*Infinity*: If a number goes outside the above limit, it will be either`Infinity`

or`-Infinity`

. We can check for this case using the function`Number.isFinite`

. A few common cases involving Infinity are:`1 / 0 == Infinity`

, and`1 / Infinity == 0`

.*NaN*:`NaN`

is anything that is “Not a Number”. If you attempt to convert an invalid non-number into a number, you will get`NaN`

. Instead of throwing an error, any arithmetic operation with`NaN`

will result in`NaN`

. We can check if a number is NaN using`Number.isNaN`

.

We can create numbers in a few ways:

```
const num1 = 123; // Literal declaration
const num2 = Number(123); // Using the Number constructor
const num3 = Number.parseInt("123.45"); // Conversion to integer
const num4 = Number.parseFloat("1.23e2"); // Conversion to float
const num5 = +"123"; // unary conversion to number
```

We can also perform some basic built-in operations:

```
const a = 12;
const b = 34;
// addition
a + b; // 46
// subtraction
a - b; // -22
// multiplication
a * b; // 408
// division
a / b; // 0.35294117647058826
// exponentiation
b ** a; // 2386420683693101000
// increment
a++; // 13
// decrement
b--; // 33
// modulus (remainder of the division)
b % a; // 10
```

There are also some binary operations we can use, but be careful, these truncate both terms to signed integers:

```
// bit shift left
34 << 12; // 139264
// bit shift right
257 >> 4; // 16
// unsigned bit shift
-1 >>> 2; // 1073741823
// bitwise or
37 | 12; // 45
// bitwise and
124 & 43; // 40
// bitwise xor
124 ^ 43; // 87
// bitwise not (signed)
~5; // -6
```

More complicated operations are available through the built-in Math library:

```
Math.sin((Math.PI * 11) / 3) / Math.sqrt(3); // -0.5
```

## 2. String

Strings are always declared through quotations:

```
const s1 = "this is a string"; // double quotes
const s2 = 'this is also a string'; // single quotes
const s3 = `this is, once more, a string`; // backticks
```

Single and double quoted strings are identical in JavaScript. Backtick quotes are template literals, allowing for extended functionality seen below:

```
const s4 = ` a
b
c`; // multiline strings
const tmp = 1 + 2;
const s5 = ` 1 + ${1 + 1} = ${tmp} `; // embedded expressions and variables
s5 === " 1 + 2 = 3 "; // true
```

Any legal expression can be embedded within the braces in backtick strings, including function calls, variables, and even other strings.

Strings can also be concatenated with the addition operator:

```
const s6 = "string1" + " " + "string2"; // "string1 string2"
```

## 3. Boolean

Booleans are the logical values, either `true`

or `false`

. They are the result of logical comparisons:

```
const b1 = !false; // true
const b2 = true && false; // false
const b3 = false || true; // true
const b4 = 123 === "456"; // false
const b5 = 1.23 === 123e-2; // true
```

## 4. Symbol

Symbols are unique values created from string keys. Two Symbols created from the same key are not equal.

```
Symbol("123") === Symbol("456"); // false
Symbol("1") === Symbol("1"); // false
const x = Symbol("abc");
x === x; // true
```

There is also a Symbol registry which is shared throughout the entire JavaScript process. Symbols you create will not occur in the registry. Instead, you must retrieve them with `Symbol.for`

. If you attempt to retrieve a Symbol that does not exist in the registry, one will be added and all subsequent requests for that key will return that Symbol.

```
Symbol("123") === Symbol.for("123"); // false
Symbol.for("123") === Symbol.for("123"); // true
Symbol.for("123") === Symbol.for("456"); // false
```

Lastly, you can check if a Symbol is from the registry with `Symbol.keyFor`

, which will check the registry for a Symbol, and return its key if it exists, and `undefined`

otherwise.

```
const mySymbol = Symbol("myKey");
const theirSymbol = Symbol.for("myKey");
mySymbol === theirSymbol; // false
Symbol.keyFor(mySymbol); // undefined
Symbol.keyFor(theirSymbol); // "myKey"
```

## 5. Object

Objects are collections of key/value pairs, where the keys are strings and the values can be any type, even other objects. Object literals are defined by the list of pairs `key: value`

, comma-separated, enclosed by curly braces.

Values can be accessed from objects with the dot operator followed by the key name, or square brackets enclosing the key as a string.

```
const myObject = { first: "123", second: 456, third: true };
myObject.first; // "123"
let second = "first";
// Dot accesses must be literal, not variables
myObject.second; // 456
// bracket accesses can be variables
myObject["first"] === myObject[second]; // true
// You can also write onto objects
myObject.first = 12;
myObject["first"]; // 12
```

## 6. undefined

`undefined`

is a global variable which represents the non-existence of data. When you attempt to access a key on an Object which does not exist, the result will be `undefined`

.

```
false === undefined; // false
({ a: "b" }["otherkey"] === undefined); // true
```

The `void`

keyword can be used to ignore the output of an expression. Writing `void x`

or `void(x)`

will evaluate `x`

, and return undefined

```
function f() {}
undefined === void f(); // true, and f gets called
```

## 7. null

`null`

is used to represent the absence of identity, and can only come from a literal expression.

```
let x = null;
```

`null`

is often used to indicate that something may be expected, but is currently unavailable. For example, if a database is represented as an object, and keys are added whenever new data is received, the expected keys could be initialized to `null`

. That way if a key is accessed, the user knows that there is nothing *yet*, but the key was correct.

Be careful when comparing `null`

and `undefined`

, as loose inequality will hold between them:

```
null == undefined; // true
undefined == null; // true
undefined === null; // false
```