[JS IR] Add descriptive error message for js("...") call

Report a message instead of NPE if `js("...")`` code couldn't be emitted

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrElementToJsExpressionTransformer.kt

@@ -192,7 +192,9 @@ class IrElementToJsExpressionTransformer : BaseIrElementToJsNodeTransformer<JsEx
 
     override fun visitCall(expression: IrCall, context: JsGenerationContext): JsExpression {
         if (context.checkIfJsCode(expression.symbol)) {
-            val statements = translateJsCodeIntoStatementList(expression.getValueArgument(0) ?: error("JsCode is expected"))!!
+            val statements = translateJsCodeIntoStatementList(expression.getValueArgument(0) ?: error("JsCode is expected"))
+                ?: error("Cannot compute js code for ${expression.render()}")
+
             if (statements.isEmpty()) return JsPrefixOperation(JsUnaryOperator.VOID, JsIntLiteral(3)) // TODO: report warning or even error
 
             val lastStatement = statements.last()

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrElementToJsStatementTransformer.kt

@@ -133,7 +133,8 @@ class IrElementToJsStatementTransformer : BaseIrElementToJsNodeTransformer<JsSta
 
     override fun visitCall(expression: IrCall, data: JsGenerationContext): JsStatement {
         if (data.checkIfJsCode(expression.symbol)) {
-            val statements = translateJsCodeIntoStatementList(expression.getValueArgument(0) ?: error("JsCode is expected"))!!
+            val statements = translateJsCodeIntoStatementList(expression.getValueArgument(0) ?: error("JsCode is expected"))
+                ?: error("Cannot compute js code for ${expression.render()}")
             return when (statements.size) {
                 0 -> JsEmpty
                 1 -> statements.single().withSource(expression, data)