fix(csv-stringify): do not alter the source record when columns is set

packages/csv-stringify/lib/api/index.js

@@ -113,11 +113,11 @@ const stringifier = function (options, state, info) {
       if (Array.isArray(chunk)) {
         // We are getting an array but the user has specified output columns. In
         // this case, we respect the columns indexes
-        if (columns) {
-          chunk.splice(columns.length);
-        }
+        const length = columns
+          ? Math.min(chunk.length, columns.length)
+          : chunk.length;
         // Cast record elements
-        for (let i = 0; i < chunk.length; i++) {
+        for (let i = 0; i < length; i++) {
           const field = chunk[i];
           const [err, value] = this.__cast(field, {
             index: i,

packages/csv-stringify/test/option.columns.ts

@@ -128,6 +128,29 @@ describe("Option `columns`", function () {
       );
     });
 
+    it("input array is not altered", function (next) {
+      const records = [
+        ["a", "b", "c"],
+        ["d", "e", "f"],
+      ];
+      stringify(
+        records,
+        {
+          columns: ["FIELD_1", "FIELD_2"],
+        },
+        (err, data) => {
+          if (!err) {
+            data.should.eql("a,b\nd,e\n");
+            records.should.eql([
+              ["a", "b", "c"],
+              ["d", "e", "f"],
+            ]);
+          }
+          next(err);
+        },
+      );
+    });
+
     it("is a readable stream", function (next) {
       const ws = stringify(
         {