Quartz 5

JavaScript Variables

2 min read

JavaScript Variables

Types

Numbers

JavaScript uses 64 bits to store number values

Fractional numbers

console.log(9.81)

Scientific notation

console.log(2.998e8)

Special Numbers

Infinity

Infinity and -Infinity represent positive and negative infinities

console.log(Infinity - 1)
console.log(Infinity + 1)
console.log(-Infinity - 1)
console.log(-Infinity + 1)

NaN

Not a number. The returned result if you try to do mathematical nonsense

console.log(0/0)
console.log(Infinity - Infinity)

Strings

Following are acceptable strings

console.log(`Down on the sea`)
console.log("Lie on the ocean")
console.log('Float on the ocean')

Backslash escapes characters

console.log("This is the first line\nAnd this is the second")
console.log("A newline character is written like \"\\n\".")

Backtick quoted strings ([[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template\_literals]\[template literals]]) can span lines and also embed other values. ${} in a template literal will be computed and converted to a string

console.log(`This is a
backtick quotes string`)
console.log(`half of 100 is ${100 / 2}`)

Boolean

console.log(3 > 2)
console.log(3 < 2)

Strings can also be compared

console.log("Aardvark" < "Zoroaster")

Uppercase characters are always less than lower case characters, so “Z” < “a”. Non alphabetic characters are less than alphabetic characters

console.log("Zebra" < "aardvark")
console.log("!" < "aardvark")
console.log("!" < "Zebra")
console.log("3" < "Zebra")
console.log("!" < "3")

Empty values

There are two special empty values, null & undefined that denote the absence of any meaningful value. They can be used interchangeably and are an [[https://medium.com/@stephenthecurt/a-brief-history-of-null-and-undefined-in-javascript-c283caab662e]\[accident of JavaScripts design]].

console.log(null == undefined);

ES6

Symbols

They are tokens that serve as unique IDs. You create symbols via the factory function Symbol() (which is loosely similar to String returning strings if called as a function):

const symbol1 = Symbol();

Add a description

const tralala = Symbol('tralala')
console.log(tralala) // Symbol(tralala)

Convert to string

const tralala = Symbol('tralala')
console.log(String(tralala)) // `Symbol(tralala)`

Every Symbol is unique

console.log(Symbol() === Symbol()) // false

Property keys

const KEY = Symbol();
const obj = {};
 
obj[KEY] = 123;
console.log(obj[KEY]); // 123
const FOO = Symbol();
const obj = {
    [FOO]() {
        return 'bar';
    }
};
console.log(obj[FOO]()); // bar

Graph View