Literals

Integers

Three types:

1. Hexadecimal (base 16): a token matching the regex ^0x[A-Fa-f0-9]+.
2. Octal (base 8): a token matching the regex ^0[0-7]+. If a token has a leading zero, but also has any 8 or 9 digits, it will be interpreted as a decimal.
3. Decimal (base 10): a token matching the regex [0-9]+.

Strings

Along with several character code escape sequences:

1. Octal: Character codes between 0 and 255 (inclusive) can be represented by a backslash followed by one to three octal digits. E.g., "\123" == "S" and "\12" == "\n". The interpretation is greedy, so it will consume as many octal digits after the backslash as it can, i.e., "\127" == "W", but "\128" == "\n8", since 8 is not an octal digit.
2. Hexadecimal: The same characters, those between 0 and 255, inclusive, can be represented by hexadecimal escapes, too. These have the prefix \x, and always require both digits. E.g., "\xFE" == "þ", "\x0a" == "\n".
3. Unicode: All Unicode characters in the basic plane (0 through 65535) can be represented with the prefix \u, followed by four hexadecimal digits. E.g., "\u00FE" == "þ".

ES6 / ES7

• es6-features.org is a good reference.
• When merging with the object rest spread operator, last assignment wins. var l = {a: 1, b: 7}; var r = {a: 5, c: 10}; {...l, ...r} > { a: 5, b: 7, c: 10 } {...r, ...l} > { a: 1, c: 10, b: 7 } {...l, ...r, a: 100} > { a: 100, b: 7, c: 10 } {a: 100, ...l, ...r} > { a: 5, b: 7, c: 10 }
• Default function parameters are evaluated at runtime. Thus, you can use mutable values, like Arrays, and mutate them without fear. Or you can use function calls, and they will be evaluated lazily as needed. function defaultNumber() { console.log('creating default number'); return 100; } function printNumber(x = defaultNumber()) { console.log('x =', x); } printNumber(22); > x = 22 printNumber(33); > x = 33 printNumber(); > creating default number > x = 100

  This demonstrates that defaultNumber() does not get called when the module is loaded, nor when printNumber(someX) is called, but only when printNumber() is called without a value.