Themes page throws console error when there is only one installed theme

[kouratoras]

In WordPress 4.9 fresh installation, when there is only one theme available in Themes page, a console error is thrown.

Steps to reproduce

1. Install WordPress
2. Go to Themes page
3. Remove TwentySixteen and TwentyFifteen, so TwentySeventeen is the only installed theme
4. Refresh the Themes page

What I see: The page is throwing a console error:

Uncaught TypeError: Cannot read property 'doSearch' of undefined
    at Object.init (load-scripts.php?c=1&load[]=hoverIntent,common,admin-bar,thickbox,underscore,backbone,wp-util,wp-backbone,wp-a11y,customize-base,theme,updates,svg-painter,h&load[]=eartbeat,wp-auth-check&ver=4.9:355)
    at HTMLDocument.<anonymous> (load-scripts.php?c=1&load[]=hoverIntent,common,admin-bar,thickbox,underscore,backbone,wp-util,wp-backbone,wp-a11y,customize-base,theme,updates,svg-painter,h&load[]=eartbeat,wp-auth-check&ver=4.9:355)
    at i (load-scripts.php?c=1&load[]=jquery-core,jquery-migrate,utils&ver=4.9:2)
    at Object.fireWith [as resolveWith] (load-scripts.php?c=1&load[]=jquery-core,jquery-migrate,utils&ver=4.9:2)
    at Function.ready (load-scripts.php?c=1&load[]=jquery-core,jquery-migrate,utils&ver=4.9:2)
    at HTMLDocument.K (load-scripts.php?c=1&load[]=jquery-core,jquery-migrate,utils&ver=4.9:2)

[afercia]

Seems to me this was introduced in [42029]. Maybe just a matter of uppercase vs. lowercase SearchView / searchView. /cc @westonruter

[chetan200891]

Created patch for change searchView to SearchView to fix.

[westonruter]

@afercia looks like you're right. 42673.diff​ does appear to fix the issue that [42029] introduced.

It makes sense why this error is only happening when there is a single theme installed because of the condition that short-circuits when there is only one theme installed: ​https://github.com/WordPress/wordpress-develop/blob/a687253cce384f6f2e1d921ca6be639431a52e93/src/wp-admin/js/theme.js#L96-L99

When that short-circuit happens, then the searchView property never gets set, resulting in an error later when it is attempted to be accessed.

[westonruter]

In 42222:

Themes: Prevent JS error on Themes admin screen when only one theme is installed.

Amends [42029].
Props chetan200891, afercia.
See #42348.
Fixes #42673.

[dd32]

Seems fine for 4.9.1

[dd32]

In 42223:

Themes: Prevent JS error on Themes admin screen when only one theme is installed.

Amends [42029].
Props chetan200891, afercia.
See #42348, westonruter.
Merges [42222] to the 4.9 branch.
Fixes #42673.