Options for formatting and parsing are available isq.config.options. You can modify these properties directly, but making global changes is consider bad form. It's better to simply override when parsing/formatting, such as

isq('.5 km', { leadingDigit: false})

Parsing options

Option	Default	Description
implicitMultiplication	true	Allow number followed by a unit to be a multiplication operation, 5 km is equivalent to 5 * km.
leadingDigit	true	Require a number to start with a digit

Formatting options

Option	Default	Description
decimalMark	'.'	The string to use representation fractional part of a number. Some locales like a comma for numbers, such a '1,23'.
exponentMark	'^'	The string that represents an exponent. Only used for numbers when unicodeSuperscript is false.
powersOf10	true	Exact powers of 10 are shown as an exponent, such as 10³ or 10^3 for 1000.
unicodeSuperscript	true	Use uncode superscript code points to represent a numeric exponent.
bestSymbol	true	Finds the best symbol to represent the value. If false, it is represented in SI base units, 1 km vs. 10³ m.
system	'SI'	The measurement system that contains the bestSymbol.
ignoreSymbols	['deca', 'hecto', 'deci']	Symbols starting with these names will not be used; 80 cm will not be shown as 8 dm.
minDigitsForSeparation	5	The minimum number of digits before group separation occurs; 1234 vs 12 345.
uncertaintyPrecision	2	The maximun number of significant digits for the uncertainty of a number.