docs: describe set array behaviour

Author: sagold

README.md

@@ -117,6 +117,29 @@ const data = pointer.set({}, ['list', '[]', 'value'], 42);
 console.log(data); // output: { list: [ { value: 42 } ] }
 ```
 
+#### array
+
+Per default `set` creates objects for each each missing data. Thus, a pointer to `/list/1` will create an object with `{ list: { 1: {} } }`. If you want to specify array-data you will need to wrap the array-index in array-brackets:
+
+```ts
+pointer.set({}, '/list/[1]', 42);
+// { list: [, 42] }
+```
+
+Omitting the index from the array-brackets will **append** the item:
+
+```ts
+pointer.set({}, '/list/[]', 42);
+// { list: [42] }
+```
+
+which also works for existing lists:
+
+```ts
+pointer.set({ list: ["first"] }, '/list/[]', 42);
+// { list: ["first", 42] }
+```
+
 
 ### remove
 

test/unit/set.test.ts

@@ -69,6 +69,13 @@ describe("pointer.set", () => {
         expect(result.array[1]).to.be.true;
     });
 
+    it("should append item to array", () => {
+        const result = set<{ array?: Array<any> }>({ array: ["first"] }, "/array/[]", "next");
+
+        expect(result.array).to.be.an("array");
+        expect(result.array).to.deep.equal(["first", "next"])
+    });
+
     it("should insert array in array", () => {
         const result = set<{ array?: Array<any> }>({}, "/array/[]/[]", true);
 
@@ -124,7 +131,6 @@ describe("pointer.set", () => {
                 "#/array/[1]/valid",
                 true
             );
-
             expect(result.array.length).to.eq(2);
             expect(result.array[1]).to.be.an("object");
             expect(result.array[1].valid).to.be.true;