javascript regex select text in [] from a string

Regex to match a decimal integer or floating point "number":

Crafting an accurate regex to match a "number" is not as simple as it may first appear! (Just ask tchrist who explained it quite thoroughly in his excellent: "What’s a Number?" answer). For the purpose of the answer here, lets assume a "number" is defined as follows:

• All numbers are decimal and no suffixes are allowed. (No octal, hex or binary numbers.)
• The integer, fraction and exponent parts consist of a sequence of decimal digits.
• The integer and exponent parts may be prefixed with an optional plus or minus sign and may have leading zeroes.
• Either the integer part or the fraction part may be missing, but not both.
• The exponent part is optional.

Given these requirements, here are examples of valid "number" representations, divided into two types; Type 1: numbers having an integer portion and Type 2: numbers without an integer portion.

Type 1: Required integer part. Optional decimal point with optional fractional digits and optional exponent:

1 +1 -1
1. +1. -1.
1.1 +1.1 -1.1
1E1 1E+1 1E-1
1.E1 1.E+1 1.E-1
1.1E1 1.1E+1 1.1E-1

Type 2: No integer part. Required decimal point and fractional digits. Optional exponent.

.1 +.1 -.1
.1E1 .1E+1 .1E-1

Here is a regex which matches all of the above number representations (written in PHP free-spacing format for readability):

$re_number = '/
    # Match a decimal integer or floating point "number".
    [+\-]?      # Optional leading sign.
    (?:         # Non-capture group for types 1 & 2.
      \b        # Either type 1: Number has integer part.
      [0-9]+    # Required whole integer part.
      (?:       # Optional fractional part.
        \.      # Required decimal point.
        [0-9]*  # Zero or more fractional digits.
      )?        # Fractional part is optional.
    |           # or Type 2: Number has no integer part.
      \B        # Leading "." is NOT on a word boundary.
      \.        # Required decimal point.
      [0-9]+    # Required fractional digits.
    )           # End group of type 1 & 2 alternatives.
    (?:         # Optional exponent.
      [Ee]      # Exponent begins with required literal E
      [+\-]?    # Optional leading sign.
      [0-9]+    # Required exponent number part.
    )?          # End optional exponent.
    /x';

Here is the same regex in Javascript syntax (with all comments removed):

var re_number =
    /[+\-]?(?:\b[0-9]+(?:\.[0-9]*)?|\B\.[0-9]+)(?:[Ee][+\-]?[0-9]+)?/;

Solution to OP question:

The OP wants to match either one or two "numbers" enclosed within square brackets. If there are two numbers, they are separated by a dash. Given the above defintion of a "number", here is a regex solution which meets these requirements:

$re_1_or_2_numbers_in_brackets = '/
    # Match one or two "numbers" inside square brackets.
    \[            # Literal left opening square bracket.
    [+\-]?        # Optional leading sign.
    (?:           # Non-capture group for types 1 & 2.
      \b          # Either type 1: Number has integer part.
      [0-9]+      # Required whole integer part.
      (?:         # Optional fractional part.
        \.        # Required decimal point.
        [0-9]*    # Zero or more fractional digits.
      )?          # Fractional part is optional.
    |             # or Type 2: Number has no integer part.
      \B          # Leading "." is NOT on a word boundary.
      \.          # Required decimal point.
      [0-9]+      # Required fractional digits.
    )             # End group of type 1 & 2 alternatives.
    (?:           # Optional exponent.
      [Ee]        # Exponent begins with required literal E
      [+\-]?      # Optional leading sign.
      [0-9]+      # Required exponent number part.
    )?            # End optional exponent.
    (?:           # Group for optional second "number".
      -           # Required - separator for second number.
      [+\-]?      # Optional leading sign.
      (?:         # Non-capture group for types 1 & 2.
        \b        # Either type 1: Number has integer part.
        [0-9]+    # Required whole integer part.
        (?:       # Optional fractional part.
          \.      # Required decimal point
          [0-9]*  # Zero or more fractional digits.
        )?        # Fractional part is optional.
      |           # or Type 2: Number has no integer part.
        \B        # Leading "." is NOT on a word boundary.
        \.        # Required decimal point.
        [0-9]+    # Required fractional digits.
      )           # End group of type 1 & 2 alternatives.
      (?:         # Optional exponent.
        [Ee]      # Exponent begins with required literal E
        [+\-]?    # Optional leading sign.
        [0-9]+    # Required exponent number part.
      )?          # End optional exponent.
    )?            # Second number is optional.
    \]            # Literal right closing square bracket.
    /x';

Here is the same regex in Javascript syntax (with all comments removed):

var re_1_or_2_numbers_in_brackets =
    /\[[+\-]?(?:\b[0-9]+(?:\.[0-9]*)?|\B\.[0-9]+)(?:[Ee][+\-]?[0-9]+)?(?:-[+\-]?(?:\b[0-9]+(?:\.[0-9]*)?|\B\.[0-9]+)(?:[Ee][+\-]?[0-9]+)?)?\]/;

This solution correctly matches all of the following variations:

[1-1] [+1-+1] [-1--1]
[1.-1.] [+1.-+1.] [-1.--1.]
[1.1-1.1] [+1.1-+1.1] [-1.1--1.1]
[1E1-1E1] [1E+1-1E+1] [1E-1-1E-1]
[1.E1-1.E1] [1.E+1-1.E+1] [1.E-1-1.E-1]
[1.1E1-1.1E1] [1.1E+1-1.1E+1] [1.1E-1-1.1E-1]
[.1-.1] [+.1-+.1] [-.1--.1]
[.1E1-.1E1] [.1E+1-.1E+1] [.1E-1-.1E-1]