js,jsdom: Canvas & context API; Added TypeSymbol.is_js_compatible & temporary hacks for JS ifaces (#12526)

vlib/builtin/js/jsfns.js.v

@@ -57,6 +57,34 @@ pub interface JS.Map {
 
 pub interface JS.Any {}
 
+pub fn js_is_null(x JS.Any) bool {
+	res := false
+	#res.val = x === null
+
+	return res
+}
+
+pub fn js_is_undefined(x JS.Any) bool {
+	res := false
+	#res.val = x === undefined
+
+	return res
+}
+
+pub fn js_null() JS.Any {
+	mut obj := JS.Any{}
+	#obj = null;
+
+	return obj
+}
+
+pub fn js_undefined() JS.Any {
+	mut obj := JS.Any{}
+	#obj = undefined;
+
+	return obj
+}
+
 pub interface JS.Array {
 	JS.Any // map(fn (JS.Any) JS.Any) JS.Array
 	map(JS.Any) JS.Array