cockpit.js: Page Location and Jumping Page location and navigation between components

## Page location

    location = cockpit.location
    cockpit.location = "/path"

Cockpit components often have different views, without changing the HTML file that is being viewed. These are known as pages. `cockpit.location` is an object that can be used to read the current page and to navigate to a different page location. It works by updating `window.location.hash`.

The `cockpit.location` looks like a HTTP path with a possible query string:

    /path/sub/page?option=value,option2

The `location.path` and `location.options` contain a parsed form of the location. While the location cannot be modified in place, a new one can be created by assigning a string to `cockpit.location` or by calling the `location.go()` function.

`cockpit.location` is designed similarly to `window.location` in that the location object is preplaced whenever the current page location changes. To be aware of when the page location changes listen for the `cockpit.onlocationchanged` event.

Using the location object as a string will result in the `location.href`.

### location.href

The string representation of this page location, including any options.

### location.path

An array of path segments, parsed and decoded appropriately. An empty array denotes the root path.

### location.options

A javascript object containing the various options present in the location.

If an option appears more than once, its value will be an array.

### location.go()

    location.go(path, [options])

Changes the current location to the given `path` and `options`. If the `path` argument is a string, it will be parsed into a path. If it is a relative path, then the result will be relative to the current `location.path`. If the `path` argument is an array of path segments, it will be treated as a full parsed absolute path.

Any options found in a `path` will be added to those in the optional `options` argument, and used in the result.

The location change will only take effect if the location has not changed in the meantime. This can be to good effect by saving a `cockpit.location` object and doing a conditional navigation, by calling the saved `location.go()` method later. This will only navigate if the user or other code has not navigated in the meantime.

### location.replace()

    location.replace(path, [options])

Similar to `location.go()` except the location change will not result in a navigation change in the browser's history.

### location.decode()

    path = location.decode(href, [options])

Decode a cockpit href into its `path` array. If the `options` argument is specified, then it will be populated with options found in the href.

If href is a relative path it will be resolved relative to `location.href`.

### location.encode()

    href = location.encode(path, [options])

Encode the given `path` and `options` into a cockpit href. The `path` argument may be an array of path segments, or a string path. If a relative path is passed, it will be resolved relative to `location.href`.

### cockpit.onlocationchanged

    cockpit.addEventListener("locationchanged", function() { ... })

An event emitted when over the `cockpit.location` changes. Typically a component reacts to this event by updating its interface to reflect the new `cockpit.location.path` and `cockpit.location.options`.

This event is not triggered immediately during a `location.go()` or similar call. It will be triggered asynchronously at a later time.

## Jumping between components

    cockpit.jump("/system/log")

In Cockpit in there multiple components shown. In order to tell Cockpit to jump to and show another component and a certain location within that component, use the `cockpit.jump()` function. Stable component paths are documented. Don't assume you can navigate into paths that are not stable API.

### cockpit.jump()

    cockpit.jump(path, [ host ])

Ask Cockpit to jump to another component. The location of the current component will not be affected. The `path` argument can be a string path, starting with `/` or an array containing the parts of a path that will be joined to create a path. If `host` is not specified, then the component on the same host as the caller will be displayed. If host is null, then the host portion of the path will be removed, displaying the component on the host that cockpit is connected directly to. This is mostly useful for displaying a dashboard or other multi-machine components.

If the calling component is not running within Cockpit, or the calling component is not currently displayed, then the jump will not happen, and this function has no effect.

### cockpit.hidden

A boolean property that indicates if the current component page is visible or hidden. When the code or user jumps to another component, the prior one remains loaded and initialized but is hidden. Use this property together with the `cockpit.onvisibilitychange` event to decide whether or not to perform expensive tasks to update the interface.

This property is analogous to the `document.hidden` page visibility API, but works with the document and frame implementation of Cockpit.

### cockpit.onvisibilitychange

    cockpit.onvisibilitychange = function() { ... }

This event is emitted when the `cockpit.hidden` property changes. This event is similar to the `document.onvisibilitychange` API, but works with the document and frame implementation of Cockpit.