[closes #11625 and closes #2488]add global and threadvar(with --threads:off mode ) pragmas supports for JS backend (#15772)

* add global pragma support for js backend

* globalThis

* add support for threadvar

* more tests

* Update compiler/jsgen.nim

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

compiler/jsgen.nim

@@ -1736,6 +1736,7 @@ proc genVarInit(p: PProc, v: PSym, n: PNode) =
     varCode: string
     varName = mangleName(p.module, v)
     useReloadingGuard = sfGlobal in v.flags and p.config.hcrOn
+    useGlobalPragmas = sfGlobal in v.flags and ({sfPure, sfThread} * v.flags != {})
 
   if v.constraint.isNil:
     if useReloadingGuard:
@@ -1743,6 +1744,10 @@ proc genVarInit(p: PProc, v: PSym, n: PNode) =
       lineF(p, "if ($1 === undefined) {$n", varName)
       varCode = $varName
       inc p.extraIndent
+    elif useGlobalPragmas:
+      lineF(p, "if (globalThis.$1 === undefined) {$n", varName)
+      varCode = $varName
+      inc p.extraIndent
     else:
       varCode = "var $2"
   else:
@@ -1795,7 +1800,7 @@ proc genVarInit(p: PProc, v: PSym, n: PNode) =
     else:
       line(p, runtimeFormat(varCode & " = $3;$n", [returnType, v.loc.r, s]))
 
-  if useReloadingGuard:
+  if useReloadingGuard or useGlobalPragmas:
     dec p.extraIndent
     lineF(p, "}$n")
 

tests/js/tglobal.nim

@@ -0,0 +1,30 @@
+block global:
+  proc getState(): int =
+    var state0 {.global.}: int
+    inc state0
+    result = state0
+
+  for i in 0 ..< 3:
+    doAssert getState() == i + 1
+
+  for i in 0 ..< 3:
+    once:
+      doAssert i == 0
+
+
+block threadvar:
+  proc getThreadState0(): int =
+    var state0 {.threadvar.}: int
+    inc state0
+    result = state0
+
+  for i in 0 ..< 3:
+    doAssert getThreadState0() == i + 1
+
+  proc getThreadState1(): int =
+    var state1 {.threadvar.}: int
+    inc state1
+    result = state1
+
+  for i in 0 ..< 3:
+    doAssert getThreadState1() == i + 1