All: Migrate away from deprecated/removed Core APIs

Summary of the changes:

* Build: Add jQuery 3.2.0-3.4.1 to versions UI can be tested against
* Build: Load jQuery & Migrate via HTTPS
* Build: Add package-lock.json to .gitignore
* Build: Update jQuery Migrate from 3.0.0 to 3.1.0
* Build: Allow to run tests against jQuery 3.x-git
* Build: Fix formatting according to JSCS rules
* Build: Disable JSCS for the inlined jQuery Color
* All: Switch from $.isArray to Array.isArray (jQuery.isArray will be
  removed in jQuery 4.0)
* All: Switch from `$.isFunction( x )` to `typeof x === "function"`
  (jQuery.isFunction will be removed in jQuery 4.0)
* All: Inline jQuery.isWindow as it'll be removed in jQuery 4.0
* Effects: Fix a timing issue in a variable declaration. Previously,
  a jQuery object was created, chained & assigned to a variable that
  was then accessed in a callback used inside of this chained
  definition. Due to a timing difference in when the callback fired for
  the first time in latest jQuery master, it was being called before
  the variable was defined.
* Tests: Make dialog & draggable unit tests less strict (newest jQuery
  returns fractional results in some cases, making comparisons fail when
  there's a tiny difference)
* All: Migrate from $.trim to bare String.prototype.trim (jQuery.trim
  will be deprecated in jQuery 3.5)

Closes gh-1901

1 files changed, 2 insertions, 1 deletions

diff --git a/ui/widgets/button.js b/ui/widgets/button.js
index 42cfec06d..3def0f9aa 100644
--- a/ui/widgets/button.js
+++ b/ui/widgets/button.js
@@ -373,7 +373,8 @@ if ( $.uiBackCompat !== false ) {
 								"attempted to call method '" + options + "'" );
 						}
 
-						if ( !$.isFunction( instance[ options ] ) || options.charAt( 0 ) === "_" ) {
+						if ( typeof instance[ options ] !== "function" ||
+							options.charAt( 0 ) === "_" ) {
 							return $.error( "no such method '" + options + "' for button" +
 								" widget instance" );
 						}