Parse a URL query string

Filters, pagination and sort order all live in the query string, and reading it back into state is a job you cannot skip. The awkward parts are keys that appear more than once, keys with no value at all, and the fact that a space can arrive as + or as %20.

Implement parseQuery(search) returning a plain object. Strip one leading ? if present, then split the rest on &, ignoring empty segments so "a=1&&b=2&" is fine.

Split each segment on its **first** = only, so a value may itself contain =. A segment with no = is a flag and its value is the empty string "". Decode both key and value by first replacing every + with a space and then calling decodeURIComponent; if decoding throws on a malformed escape, use the raw text instead.

A key seen once maps to a string. A key seen two or more times maps to an array of all of its values, in order of appearance. Empty or missing input returns {}.

What it has to do

• Strip an optional leading ? and ignore empty & segments.
• Split each pair on the first = only; a key with no = gets the value "".
• Decode + as a space as well as percent escapes, on both keys and values.
• Collect repeated keys into an array in order of appearance, keeping a single occurrence as a string.
• Return {} for an empty string.

Your workspace