Literal is a value of any type given explicitly. So in expression x+10, x is variable and 10 numeric literal.
Sign + or - can be consider as part of the numeric literal or as expression with unary + and -.

undefined The undefined value means that no value was assigned. For example, you can check if a function argument is passed:
if(arg === undefined) ...
Decimal integer literal is defined as sequence of digits without a leading 0 (zero).
An octal integer literal is defined as sequence of 0-7 digits with leading 0 or prefix 0o.
A hexadecimal integer literal is defined as sequence of 0-9 digits and letters a-f or A-F with prefix 0x or 0X.
Case of letters is meaningless, so 0xa = 0xA = 10 and 0xf = 0xF = 15
A binary integer literal is defined as sequence of 0 and 1 with prefix 0b or 0B.
-3.14E+23 .14e-23

A floating-point literal is defined by formula

true and false are boolean literals. Do not confuse them with the true and false values of the Boolean object. The Boolean object is a wrapper around the primitive boolean data type.
[1,2 , 3]
[ "a", , "c"]
An array literal is defined as sequence of values in square braces. When value is omitted, it means an undefined value.
  prop1: 23,
  fun1 : function() 
       {return 1;},
  arr: [1,2,3],
  obj: {a: "a", b: "b"}
An object literal is a list of zero or more pairs of property names and associated values of an object, enclosed in curly braces. Values also can be object, function or array.
A string literal is a sequence of characters in single or double quotes. More details here
/^\S+@\S+$/ A regular expression literal is defined as a pattern enclosed between slashes, with possible flags at end