Two correctness fixes from the #2367 bonus findings

.changeset/destroy-instances.md

@@ -0,0 +1,5 @@
+---
+"dropzone": patch
+---
+
+Stop `destroy()` removing a different instance. `Dropzone.instances.splice(indexOf(this), 1)` dropped the last entry whenever `indexOf` returned -1 — calling `destroy()` twice was enough — evicting an unrelated live Dropzone from the registry.

.changeset/form-enctype.md

@@ -0,0 +1,5 @@
+---
+"dropzone": patch
+---
+
+Set `enctype="multipart/form-data"` on a form again. `init()` compared `tagName` against lower-case `"form"`, which never matches, so the attribute was never set. Only affects forms that are also submitted natively; the XHR upload is unchanged.

packages/dropzone/src/dropzone.ts

@@ -334,8 +334,9 @@ export default class Dropzone extends Emitter {
   // The function that gets called when Dropzone is initialized. You
   // can (and should) setup event listeners inside this function.
   init() {
-    // In case it isn't set already
-    if (this.element.tagName === "form") {
+    // In case it isn't set already. `tagName` is upper case on HTML elements,
+    // so this never matched and the attribute was never set.
+    if (this.element.tagName === "FORM") {
       this.element.setAttribute("enctype", "multipart/form-data");
     }
 
@@ -547,7 +548,11 @@ export default class Dropzone extends Emitter {
       this.hiddenFileInput = null;
     }
     delete this.element.dropzone;
-    return Dropzone.instances.splice(Dropzone.instances.indexOf(this), 1);
+    // `indexOf` returns -1 for an instance that is no longer registered --
+    // destroying twice is enough -- and `splice(-1, 1)` would then quietly
+    // drop the last entry, which is a different, live Dropzone.
+    let index = Dropzone.instances.indexOf(this);
+    return index === -1 ? [] : Dropzone.instances.splice(index, 1);
   }
 
   updateTotalUploadProgress() {

packages/dropzone/test/unit-tests/all.js

@@ -764,6 +764,24 @@ describe("Dropzone", function () {
           }, 10);
         })));
 
+    describe("init()", function () {
+      it("should set the enctype on a form element", function () {
+        let form = Dropzone.createElement("<form></form>");
+        let formDropzone = new Dropzone(form, { url: "url" });
+
+        expect(form.getAttribute("enctype")).toBe("multipart/form-data");
+        formDropzone.destroy();
+      });
+
+      it("should leave an existing enctype alone on a non-form element", function () {
+        let div = Dropzone.createElement("<div></div>");
+        let divDropzone = new Dropzone(div, { url: "url" });
+
+        expect(div.getAttribute("enctype")).toBe(null);
+        divDropzone.destroy();
+      });
+    });
+
     describe(".destroy()", function () {
       it("should properly cancel all pending uploads and remove all file references", () =>
         new Promise((done) => {
@@ -807,6 +825,18 @@ describe("Dropzone", function () {
         dropzone.destroy();
         return expect(Dropzone.instances.indexOf(dropzone) === -1).toBeTruthy();
       });
+
+      it("should leave other instances alone when destroyed twice", function () {
+        let other = new Dropzone(Dropzone.createElement("<div></div>"), { url: "url" });
+
+        dropzone.destroy();
+        // The second call finds nothing to remove. `splice(-1, 1)` used to
+        // take the last entry regardless, evicting an unrelated live instance.
+        dropzone.destroy();
+
+        expect(Dropzone.instances.indexOf(other) !== -1).toBeTruthy();
+        other.destroy();
+      });
     });
 
     describe(".filesize()", function () {