From 138bfc28090ccf03450cf02cb24f06b60f57cd3b Mon Sep 17 00:00:00 2001
From: Richard Musiol <mail@richard-musiol.de>
Date: Thu, 18 Oct 2018 15:53:38 +0200
Subject: syscall/js: make zero js.Value represent "undefined"

This commit changes the encoding of js.Value so that the zero js.Value
represents the JavaScript value "undefined". This is what users
intuitively expect.

Specifically, the encodings of "undefined" and the number zero have
been swapped.

Fixes #27592.

Change-Id: Icfc832c8cdf7a8a78bd69d20e00a04dbed0ccd10
Reviewed-on: https://go-review.googlesource.com/c/143137
Run-TryBot: Richard Musiol <neelance@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
---
 misc/wasm/wasm_exec.js | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

(limited to 'misc')

diff --git a/misc/wasm/wasm_exec.js b/misc/wasm/wasm_exec.js
index 815b3fbeff..bd9754e53a 100644
--- a/misc/wasm/wasm_exec.js
+++ b/misc/wasm/wasm_exec.js
@@ -95,6 +95,9 @@
 
 			const loadValue = (addr) => {
 				const f = mem().getFloat64(addr, true);
+				if (f === 0) {
+					return undefined;
+				}
 				if (!isNaN(f)) {
 					return f;
 				}
@@ -112,14 +115,18 @@
 						mem().setUint32(addr, 0, true);
 						return;
 					}
+					if (v === 0) {
+						mem().setUint32(addr + 4, nanHead, true);
+						mem().setUint32(addr, 1, true);
+						return;
+					}
 					mem().setFloat64(addr, v, true);
 					return;
 				}
 
 				switch (v) {
 					case undefined:
-						mem().setUint32(addr + 4, nanHead, true);
-						mem().setUint32(addr, 1, true);
+						mem().setFloat64(addr, 0, true);
 						return;
 					case null:
 						mem().setUint32(addr + 4, nanHead, true);
@@ -334,7 +341,7 @@
 			this._inst = instance;
 			this._values = [ // TODO: garbage collection
 				NaN,
-				undefined,
+				0,
 				null,
 				true,
 				false,
@@ -396,14 +403,14 @@
 		}
 
 		static _makeCallbackHelper(id, pendingCallbacks, go) {
-			return function() {
+			return function () {
 				pendingCallbacks.push({ id: id, args: arguments });
 				go._resolveCallbackPromise();
 			};
 		}
 
 		static _makeEventCallbackHelper(preventDefault, stopPropagation, stopImmediatePropagation, fn) {
-			return function(event) {
+			return function (event) {
 				if (preventDefault) {
 					event.preventDefault();
 				}
-- 
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