fix: check undefined string and show how to correct

Author: seongwon-kang

src/stripIndentTransformer/stripIndentTransformer.js

@@ -12,6 +12,11 @@ const stripIndentTransformer = (type = 'initial') => {
 
   return {
     onEndResult(endResult) {
+      if (typeof(endResult) === 'undefined') {
+        throw TypeError(`input string is undefined: Check your template string. 
+          (e.g. \\4 will throw SyntaxError with 'Octal escape sequences are not allowed')
+        `);
+      }
       if (type === 'all') {
         // remove all indentation from each line
         return endResult.replace(/^[^\S\n]+/gm, '');

src/stripIndentTransformer/stripIndentTransformer.test.js

@@ -48,3 +48,16 @@ test('throws an error if encounters invalid type', () => {
     stripIndentTransformer('blue');
   }).toThrow(/not supported/);
 });
+
+test('invalid template string should throw error message with ', () => {
+  const stripIndent = createTag(
+    stripIndentTransformer(),
+    trimResultTransformer('smart'),
+  );
+
+  const actual = () => {
+    stripIndent`
+      \4
+    `};
+  expect(actual).toThrow(`input string is undefined: Check your template string.`);
+});