method

toggle

Source

/**
 * Adds the class [value] to the element if it is not on it, removes it if it
 * is.
 *
 * If [shouldAdd] is true, then we always add that [value] to the element. If
 * [shouldAdd] is false then we always remove [value] from the element.
 *
 * If this corresponds to one element, returns `true` if [value] is present
 * after the operation, and returns `false` if [value] is absent after the
 * operation.
 *
 * If this corresponds to many elements, `null` is always returned.
 *
 * [value] must be a valid 'token' representing a single class, i.e. a
 * non-empty string containing no whitespace.  To toggle multiple classes, use
 * [toggleAll].
 */
bool toggle(String value, [bool shouldAdd]);