Quick Reference Javascript

1 Lexical Structure

1.1 Comments

// single line comment

/*
  Multi-line comment
 */

1.2 Literals

1         // Number one
1.5       // Number one point five
'Hello'   // String
true      // Boolean
false     // Boolean
null      // Null object

1.3 Declarations

var	Declares a variable, optionally initializing it to a value
let	Declares a block-scoped, local variable, optionally initializing it to a value.
const	Declares a block-scoped, read-only named constant.

2 Numbers

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Numbers_and_dates

2.1 Integer

base-10 integer

1
10
123
1000

hexadecimal literal begins with 0x or 0X

0xff      // 255
0XABCD    // 43981

In ES6, binary (base 2) or octal (base 8) using prefixes 0b/0B and 0o/0O

2.2 Floating-point

Quick Notes

Property Access

expression . identifier
expression [ expression ]

Examples

let team = {size:5}
team.size
team["size"]

Conditional Property Access

expression ?. identifier
expression ?.[ expression ]

Examples

let a = {}
a?.b        // undefined

References

https://developer.mozilla.org/en-US/docs/Web/JavaScript