v.gen.js: support global declarations in the JS backend (#10773)

vlib/v/gen/js/js.v

@@ -105,6 +105,7 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 		g.find_class_methods(file.stmts)
 		g.escape_namespace()
 	}
+
 	for file in files {
 		g.file = file
 		g.enter_namespace(g.file.mod.name)
@@ -120,6 +121,7 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 			g.gen_builtin_type_defs()
 			g.generated_builtin = true
 		}
+
 		g.stmts(file.stmts)
 		// store the current namespace
 		g.escape_namespace()
@@ -292,6 +294,7 @@ pub fn (mut g JsGen) init() {
 	g.definitions.writeln('// Generated by the V compiler\n')
 	g.definitions.writeln('"use strict";')
 	g.definitions.writeln('')
+	g.definitions.writeln('var \$global = (new Function("return this"))();')
 }
 
 pub fn (g JsGen) hashes() string {
@@ -418,6 +421,27 @@ fn (mut g JsGen) write_v_source_line_info(pos token.Position) {
 	}
 }
 
+fn (mut g JsGen) gen_global_decl(node ast.GlobalDecl) {
+	mod := if g.pref.build_mode == .build_module { 'enumerable: false' } else { 'enumerable: true' }
+	for field in node.fields {
+		if field.has_expr {
+			tmp_var := g.new_tmp_var()
+			g.write('const $tmp_var = ')
+			g.expr(field.expr)
+			g.writeln(';')
+			g.writeln('Object.defineProperty(\$global,"$field.name", {
+				configurable: false,
+				$mod ,
+				writable: true,
+				value: $tmp_var
+				}
+			); // global')
+		} else {
+			// TODO(playXE): Initialize with default value of type
+		}
+	}
+}
+
 fn (mut g JsGen) stmt(node ast.Stmt) {
 	g.stmt_start_pos = g.ns.out.len
 	match node {
@@ -480,7 +504,9 @@ fn (mut g JsGen) stmt(node ast.Stmt) {
 			g.writeln('')
 		}
 		ast.GlobalDecl {
-			// TODO
+			g.write_v_source_line_info(node.pos)
+			g.gen_global_decl(node)
+			g.writeln('')
 		}
 		ast.GotoLabel {
 			g.write_v_source_line_info(node.pos)
@@ -903,6 +929,7 @@ fn (mut g JsGen) gen_method_decl(it ast.FnDecl) {
 	if is_main {
 		// there is no concept of main in JS but we do have iife
 		g.writeln('/* program entry point */')
+
 		g.write('(')
 		if has_go {
 			g.write('async ')