fix: keep scalar json logs instead of dropping them

src/logger.ts

@@ -183,9 +183,17 @@ function processData(data: Uint8Array | string, encoding?: BufferEncoding) {
   // strip any leading ANSI color codes from the decoded data
   // to parse colored JSON objects correctly
   decodedData = decodedData.replace(/\x1b[[(?);]{0,2}(;?\d)*./g, '');
+  let parsedData;
   try {
-    return {isJSON: true, processedData: JSON.parse(decodedData)};
+    parsedData = JSON.parse(decodedData);
   } catch (e) {
     return {isJSON: false, processedData: decodedData};
   }
+  // Numbers, booleans, null and JSON strings parse successfully but they are
+  // not log objects, so there is nowhere to attach the context fields added by
+  // getJSONWithContext. Log them as plain text instead.
+  if (typeof parsedData !== 'object' || parsedData === null) {
+    return {isJSON: false, processedData: decodedData};
+  }
+  return {isJSON: true, processedData: parsedData};
 }

test/logger.ts

@@ -86,6 +86,41 @@ describe('getModifiedData', () => {
     assert.equal(modifiedData, expectedJSONOutput);
   });
 
+  it('json number value', () => {
+    const modifiedData = getModifiedData('42');
+    assert.equal(
+      modifiedData,
+      JSON.stringify(Object.assign({message: '42'}, expectedMetadata)) + '\n',
+    );
+  });
+
+  it('json boolean value', () => {
+    const modifiedData = getModifiedData('true');
+    assert.equal(
+      modifiedData,
+      JSON.stringify(Object.assign({message: 'true'}, expectedMetadata)) +
+        '\n',
+    );
+  });
+
+  it('json null value', () => {
+    const modifiedData = getModifiedData('null');
+    assert.equal(
+      modifiedData,
+      JSON.stringify(Object.assign({message: 'null'}, expectedMetadata)) +
+        '\n',
+    );
+  });
+
+  it('json string value', () => {
+    const modifiedData = getModifiedData('"abc"');
+    assert.equal(
+      modifiedData,
+      JSON.stringify(Object.assign({message: '"abc"'}, expectedMetadata)) +
+        '\n',
+    );
+  });
+
   it('json with user label', () => {
     const data = JSON.stringify({
       text: 'default text.',