jQuery deparam, opposite of $.param()

deparam.js

  // Deparam (from string)
  //
  // Deserialize a params string into an object, optionally coercing numbers,
  // booleans, null and undefined values; this method is the counterpart to the
  // internal jQuery.param method.
  //
  // Usage:
  //
  // > deparam( params [, coerce ] );
  //
  // Arguments:
  //
  //  params - (String) A params string to be parsed.
  //  coerce - (Boolean) If true, coerces any numbers or true, false, null, and
  //    undefined to their actual value. Defaults to false if omitted.
  //
  // Returns:
  //
  //  (Object) An object representing the deserialized params string.
  //
  // @see https://github.com/cowboy/jquery-bbq/blob/master/jquery.ba-bbq.js

  function deparam( params, coerce ) {
    var obj = {},
      coerce_types = { 'true': !0, 'false': !1, 'null': null };

    // Iterate over all name=value pairs.
    $.each( params.replace( /\+/g, ' ' ).split( '&' ), function(j,v){
      var param = v.split( '=' ),
        key = decodeURIComponent( param[0] ),
        val,
        cur = obj,
        i = 0,

        // If key is more complex than 'foo', like 'a[]' or 'a[b][c]', split it
        // into its component parts.
        keys = key.split( '][' ),
        keys_last = keys.length - 1;

      // If the first keys part contains [ and the last ends with ], then []
      // are correctly balanced.
      if ( /\[/.test( keys[0] ) && /\]$/.test( keys[ keys_last ] ) ) {
        // Remove the trailing ] from the last keys part.
        keys[ keys_last ] = keys[ keys_last ].replace( /\]$/, '' );

        // Split first keys part into two parts on the [ and add them back onto
        // the beginning of the keys array.
        keys = keys.shift().split('[').concat( keys );

        keys_last = keys.length - 1;
      } else {
        // Basic 'foo' style key.
        keys_last = 0;
      }

      // Are we dealing with a name=value pair, or just a name?
      if ( param.length === 2 ) {
        val = decodeURIComponent( param[1] );

        // Coerce values.
        if ( coerce ) {
          val = val && !isNaN(val)            ? +val              // number
            : val === 'undefined'             ? undefined         // undefined
            : coerce_types[val] !== undefined ? coerce_types[val] // true, false, null
            : val;                                                // string
        }

        if ( keys_last ) {
          // Complex key, build deep object structure based on a few rules:
          // * The 'cur' pointer starts at the object top-level.
          // * [] = array push (n is set to array length), [n] = array if n is
          //   numeric, otherwise object.
          // * If at the last keys part, set the value.
          // * For each keys part, if the current level is undefined create an
          //   object or array based on the type of the next keys part.
          // * Move the 'cur' pointer to the next level.
          // * Rinse & repeat.
          for ( ; i <= keys_last; i++ ) {
            key = keys[i] === '' ? cur.length : keys[i];
            cur = cur[key] = i < keys_last ? cur[key] || ( keys[i+1] && isNaN( keys[i+1] ) ? {} : [] ) : val;
          }

        } else {
          // Simple key, even simpler rules, since only scalars and shallow
          // arrays are allowed.

          if ( $.isArray( obj[key] ) ) {
            // val is already an array, so push on the next value.
            obj[key].push( val );

          } else if ( obj[key] !== undefined ) {
            // val isn't an array, but since a second value has been specified,
            // convert val into an array.
            obj[key] = [ obj[key], val ];

          } else {
            // val is a scalar.
            obj[key] = val;
          }
        }

      } else if ( key ) {
        // No value was defined, so set something meaningful.
        obj[key] = coerce ? undefined : '';
      }
    });

    return obj;
  }