From a54fe9f77c0e632163c89729d17239df1f3c3883 Mon Sep 17 00:00:00 2001
From: Lovell Fuller <github@lovell.info>
Date: Fri, 21 Dec 2018 19:54:33 +0000
Subject: [PATCH] Prevent mutatation of jpeg options #1516

---
 docs/changelog.md |  5 +++++
 lib/output.js     | 30 +++++++++++++++---------------
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/docs/changelog.md b/docs/changelog.md
index 275cb8dd..a1491ebd 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -4,6 +4,11 @@
 
 Requires libvips v8.7.0.
 
+#### v0.21.2 - TBD
+
+* Prevent mutatation of options passed to `jpeg`.
+  [#1516](https://github.com/lovell/sharp/issues/1516)
+
 #### v0.21.1 - 7<sup>th</sup> December 2018
 
 * Install: support `sharp_dist_base_url` npm config, like existing `SHARP_DIST_BASE_URL`.
diff --git a/lib/output.js b/lib/output.js
index 58849854..a3aad553 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -175,30 +175,30 @@ function jpeg (options) {
         throw new Error('Invalid chromaSubsampling (4:2:0, 4:4:4) ' + options.chromaSubsampling);
       }
     }
-    options.trellisQuantisation = is.bool(options.trellisQuantization) ? options.trellisQuantization : options.trellisQuantisation;
-    if (is.defined(options.trellisQuantisation)) {
-      this._setBooleanOption('jpegTrellisQuantisation', options.trellisQuantisation);
+    const trellisQuantisation = is.bool(options.trellisQuantization) ? options.trellisQuantization : options.trellisQuantisation;
+    if (is.defined(trellisQuantisation)) {
+      this._setBooleanOption('jpegTrellisQuantisation', trellisQuantisation);
     }
     if (is.defined(options.overshootDeringing)) {
       this._setBooleanOption('jpegOvershootDeringing', options.overshootDeringing);
     }
-    options.optimiseScans = is.bool(options.optimizeScans) ? options.optimizeScans : options.optimiseScans;
-    if (is.defined(options.optimiseScans)) {
-      this._setBooleanOption('jpegOptimiseScans', options.optimiseScans);
-      if (options.optimiseScans) {
+    const optimiseScans = is.bool(options.optimizeScans) ? options.optimizeScans : options.optimiseScans;
+    if (is.defined(optimiseScans)) {
+      this._setBooleanOption('jpegOptimiseScans', optimiseScans);
+      if (optimiseScans) {
         this.options.jpegProgressive = true;
       }
     }
-    options.optimiseCoding = is.bool(options.optimizeCoding) ? options.optimizeCoding : options.optimiseCoding;
-    if (is.defined(options.optimiseCoding)) {
-      this._setBooleanOption('jpegOptimiseCoding', options.optimiseCoding);
+    const optimiseCoding = is.bool(options.optimizeCoding) ? options.optimizeCoding : options.optimiseCoding;
+    if (is.defined(optimiseCoding)) {
+      this._setBooleanOption('jpegOptimiseCoding', optimiseCoding);
     }
-    options.quantisationTable = is.number(options.quantizationTable) ? options.quantizationTable : options.quantisationTable;
-    if (is.defined(options.quantisationTable)) {
-      if (is.integer(options.quantisationTable) && is.inRange(options.quantisationTable, 0, 8)) {
-        this.options.jpegQuantisationTable = options.quantisationTable;
+    const quantisationTable = is.number(options.quantizationTable) ? options.quantizationTable : options.quantisationTable;
+    if (is.defined(quantisationTable)) {
+      if (is.integer(quantisationTable) && is.inRange(quantisationTable, 0, 8)) {
+        this.options.jpegQuantisationTable = quantisationTable;
       } else {
-        throw new Error('Invalid quantisation table (integer, 0-8) ' + options.quantisationTable);
+        throw new Error('Invalid quantisation table (integer, 0-8) ' + quantisationTable);
       }
     }
   }