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Event: Simulate focus/blur in IE via focusin/focusout
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In IE (all versions), `focus` & `blur` handlers are fired asynchronously
but `focusin` & `focusout` are run synchronously. In other browsers, all
those handlers are fired synchronously. Asynchronous behavior of these
handlers in IE caused issues for IE (gh-4856, gh-4859).

We now simulate `focus` via `focusin` & `blur` via `focusout` in IE to avoid
these issues. This also let us simplify some tests.

This commit also simplifies `leverageNative` - with IE now using `focusin`
to simulate `focus` and `focusout` to simulate `blur`, we don't have to deal
with async events in `leverageNative`. This also fixes broken `focus` triggers
after first triggering it on a hidden element - previously, `leverageNative`
assumed that the native `focus` handler not firing after calling the native 
`focus` method meant it would be handled later, asynchronously, which
was not the case (gh-4950).

Fixes gh-4856
Fixes gh-4859
Fixes gh-4950
Closes gh-5223

Co-authored-by: Richard Gibson <richard.gibson@gmail.com>
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@mgol @gibson042
mgol and gibson042 committed Mar 27, 2023
1 parent 992a191 commit ce60d31
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Showing 2 changed files with 258 additions and 166 deletions.
102 changes: 56 additions & 46 deletions src/event.js
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Original file line number Diff line number Diff line change
@@ -1,9 +1,9 @@
import jQuery from "./core.js";
import document from "./var/document.js";
import documentElement from "./var/documentElement.js";
import rnothtmlwhite from "./var/rnothtmlwhite.js";
import rcheckableType from "./var/rcheckableType.js";
import slice from "./var/slice.js";
import isIE from "./var/isIE.js";
import acceptData from "./data/var/acceptData.js";
import dataPriv from "./data/var/dataPriv.js";
import nodeName from "./core/nodeName.js";
Expand All @@ -21,16 +21,6 @@ function returnFalse() {
return false;
}

// Support: IE <=9 - 11+
// focus() and blur() are asynchronous, except when they are no-op.
// So expect focus to be synchronous when the element is already active,
// and blur to be synchronous when the element is not already active.
// (focus and blur are always synchronous in other supported browsers,
// this just defines when we can count on it).
function expectSync( elem, type ) {
return ( elem === document.activeElement ) === ( type === "focus" );
}

function on( elem, types, selector, data, fn, one ) {
var origFn, type;

Expand Down Expand Up @@ -459,7 +449,7 @@ jQuery.event = {
el.click && nodeName( el, "input" ) ) {

// dataPriv.set( el, "click", ... )
leverageNative( el, "click", returnTrue );
leverageNative( el, "click", true );
}

// Return false to allow normal processing in the caller
Expand Down Expand Up @@ -511,10 +501,10 @@ jQuery.event = {
// synthetic events by interrupting progress until reinvoked in response to
// *native* events that it fires directly, ensuring that state changes have
// already occurred before other listeners are invoked.
function leverageNative( el, type, expectSync ) {
function leverageNative( el, type, isSetup ) {

// Missing expectSync indicates a trigger call, which must force setup through jQuery.event.add
if ( !expectSync ) {
// Missing `isSetup` indicates a trigger call, which must force setup through jQuery.event.add
if ( !isSetup ) {
if ( dataPriv.get( el, type ) === undefined ) {
jQuery.event.add( el, type, returnTrue );
}
Expand All @@ -526,15 +516,13 @@ function leverageNative( el, type, expectSync ) {
jQuery.event.add( el, type, {
namespace: false,
handler: function( event ) {
var notAsync, result,
var result,
saved = dataPriv.get( this, type );

if ( ( event.isTrigger & 1 ) && this[ type ] ) {

// Interrupt processing of the outer synthetic .trigger()ed event
// Saved data should be false in such cases, but might be a leftover capture object
// from an async native handler (gh-4350)
if ( !saved.length ) {
if ( !saved ) {

// Store arguments for use when handling the inner native event
// There will always be at least one argument (an event object), so this array
Expand All @@ -543,28 +531,17 @@ function leverageNative( el, type, expectSync ) {
dataPriv.set( this, type, saved );

// Trigger the native event and capture its result
// Support: IE <=9 - 11+
// focus() and blur() are asynchronous
notAsync = expectSync( this, type );
this[ type ]();
result = dataPriv.get( this, type );
if ( saved !== result || notAsync ) {
dataPriv.set( this, type, false );
} else {
result = {};
}
dataPriv.set( this, type, false );

if ( saved !== result ) {

// Cancel the outer synthetic event
event.stopImmediatePropagation();
event.preventDefault();

// Support: Chrome 86+
// In Chrome, if an element having a focusout handler is blurred by
// clicking outside of it, it invokes the handler synchronously. If
// that handler calls `.remove()` on the element, the data is cleared,
// leaving `result` undefined. We need to guard against this.
return result && result.value;
return result;
}

// If this is an inner synthetic event for an event with a bubbling surrogate
Expand All @@ -582,16 +559,11 @@ function leverageNative( el, type, expectSync ) {
} else if ( saved.length ) {

// ...and capture the result
dataPriv.set( this, type, {
value: jQuery.event.trigger(

// Support: IE <=9 - 11+
// Extend with the prototype to reset the above stopImmediatePropagation()
jQuery.extend( saved[ 0 ], jQuery.Event.prototype ),
saved.slice( 1 ),
this
)
} );
dataPriv.set( this, type, jQuery.event.trigger(
saved[ 0 ],
saved.slice( 1 ),
this
) );

// Abort handling of the native event
event.stopImmediatePropagation();
Expand Down Expand Up @@ -724,6 +696,29 @@ jQuery.each( {
}, jQuery.event.addProp );

jQuery.each( { focus: "focusin", blur: "focusout" }, function( type, delegateType ) {

// Support: IE 11+
// Attach a single focusin/focusout handler on the document while someone wants focus/blur.
// This is because the former are synchronous in IE while the latter are async. In other
// browsers, all those handlers are invoked synchronously.
function focusMappedHandler( nativeEvent ) {

// `eventHandle` would already wrap the event, but we need to change the `type` here.
var event = jQuery.event.fix( nativeEvent );
event.type = nativeEvent.type === "focusin" ? "focus" : "blur";
event.isSimulated = true;

// focus/blur don't bubble while focusin/focusout do; simulate the former by only
// invoking the handler at the lower level.
if ( event.target === event.currentTarget ) {

// The setup part calls `leverageNative`, which, in turn, calls
// `jQuery.event.add`, so event handle will already have been set
// by this point.
dataPriv.get( this, "handle" )( event );
}
}

jQuery.event.special[ type ] = {

// Utilize native event if possible so blur/focus sequence is correct
Expand All @@ -732,10 +727,15 @@ jQuery.each( { focus: "focusin", blur: "focusout" }, function( type, delegateTyp
// Claim the first handler
// dataPriv.set( this, "focus", ... )
// dataPriv.set( this, "blur", ... )
leverageNative( this, type, expectSync );
leverageNative( this, type, true );

if ( isIE ) {
this.addEventListener( delegateType, focusMappedHandler );
} else {

// Return false to allow normal processing in the caller
return false;
// Return false to allow normal processing in the caller
return false;
}
},
trigger: function() {

Expand All @@ -746,6 +746,16 @@ jQuery.each( { focus: "focusin", blur: "focusout" }, function( type, delegateTyp
return true;
},

teardown: function() {
if ( isIE ) {
this.removeEventListener( delegateType, focusMappedHandler );
} else {

// Return false to indicate standard teardown should be applied
return false;
}
},

// Suppress native focus or blur if we're currently inside
// a leveraged native-event stack
_default: function( event ) {
Expand Down
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