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<!doctype html>
<html>
<body>
<p>
There are currently <span id="totalInnerHandlers">0</span> beforeunload handlers registered in this frame.
</p>
<p>
There are currently <span id="totalOuterHandlers">0</span> beforeunload handlers registered on my subframe.
</p>
<iframe src="about:blank" id="subframe"></iframe>
<script>
this.BeforeUnloader = {
_innerEventHandlers: [],
_outerEventHandlers: [],
get $totalInner() {
delete this.$totalInner;
return this.$totalInner = document.getElementById("totalInnerHandlers");
},
get $totalOuter() {
delete this.$totalOuter;
return this.$totalOuter = document.getElementById("totalOuterHandlers");
},
get $subframe() {
delete this.$subframe;
return this.$subframe = document.getElementById("subframe");
},
pushInner(howMany) {
for (let i = 0; i < howMany; ++i) {
let func = () => {};
this._innerEventHandlers.push(func);
addEventListener("beforeunload", func);
}
this.$totalInner.textContent = this._innerEventHandlers.length;
},
popInner(howMany) {
for (let i = 0; i < howMany; ++i) {
let func = this._innerEventHandlers.pop();
if (func) {
removeEventListener("beforeunload", func);
}
}
this.$totalInner.textContent = this._innerEventHandlers.length;
},
pushOuter(howMany) {
if (!this.$subframe.parentNode) {
throw new Error("Subframe I'm holding a reference to detached!");
}
for (let i = 0; i < howMany; ++i) {
let func = () => {};
this._outerEventHandlers.push(func);
this.$subframe.contentWindow.addEventListener("beforeunload", func);
}
this.$totalOuter.textContent = this._outerEventHandlers.length;
},
popOuter(howMany) {
if (!this.$subframe.parentNode) {
throw new Error("Subframe I'm holding a reference to detached!");
}
for (let i = 0; i < howMany; ++i) {
let func = this._outerEventHandlers.pop();
if (func) {
this.$subframe.contentWindow.removeEventListener("beforeunload", func);
}
}
this.$totalOuter.textContent = this._outerEventHandlers.length;
},
reset() {
this.popInner(this._innerEventHandlers.length);
this.popOuter(this._outerEventHandlers.length);
},
};
</script>
</body>
</html>
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