feat: label first-time contributor.
diff --git a/index.js b/index.js
index 95ea299..457729a 100644
--- a/index.js
+++ b/index.js
@@ -119,12 +119,17 @@
         if (isCore) {
             labelList.push('PR: author is committer');
         }
+
         const content = context.payload.pull_request.body;
         if (content && content.indexOf('[x] The API has been changed.') > -1) {
             labelList.push('PR: awaiting doc');
             commentText += '\n\n' + text.PR_AWAITING_DOC;
         }
 
+        if (await isFirstTimeContributor(context)) {
+            labelList.push('PR: first-time contributor');
+        }
+
         const comment = context.octokit.issues.createComment(
             context.issue({
                 body: commentText
@@ -234,6 +239,22 @@
     );
 }
 
+async function isFirstTimeContributor (context) {
+    try {
+        const response = await context.octokit.issues.listForRepo(
+            context.repo({
+                state: 'all',
+                creator: context.payload.pull_request.user.login
+            })
+        );
+        return response.data.filter(data => data.pull_request) === 1;
+    }
+    catch (e) {
+        logger.error('failed to check first-time contributor');
+        logger.error(e);
+    }
+}
+
 async function translateIssue (context, createdIssue) {
     if (!createdIssue) {
         return;