[TS] Add Obj API (#5788)

* added basic code

* backup work

* got class property to work

* backup progress

* implementented fmt for creating code

* added docs for genFieldUtils

* back up work

* added base helper js func

* added union js code

* added unpackTo and base for pack

* added pack code

* added null check for packing struct list

* passes compile test

* fixed some spacing of generated functions

* added annotations for constructors

* added obj api unpack test

* tested pack to work

* merge branch

* separated js and ts test

* fixed union signature to include string

* fixed generator to support string union

* hardcoded fb builder name

* refactored struct vector creation

* work around createLong

* handle default value in constructor

* update typescript docs

* added notes about import flag

* fixed formatting stuffs

* undo TypescriptTest change

* refactored fmt

* updated generated code

* remove ignoring union_vector for js

* revert changes for .project

* revert changes for package.json

* don't generate js in ts test

* fixed android project file

* removed unused js function

* removed package-lock.json

* adjust createObjList to new signature

* changed regex to callback style

* fixed package.json

* used existing func for generating annotation

* changed ternary to !!

* added return type for lambda

* removed callback style for obj api generator

* fixed js file indentation

* removed unused header

* added tests for string only union

* handle string only union and refactor union conv func

* updated generated ts files

* renamed union conv func

* made js test create files like other languages

* removed union string only handling

* don't allow null in createObjectOffsetList

* updated generated ts code

* changed the line that triggers Windows build errors

* hopefully fix CI error

docs/source/TypeScriptUsage.md

@@ -60,6 +60,38 @@ Now you can access values like this:
   let pos = monster.pos();
 ~~~
 
+## Object based API
+
+FlatBuffers is all about memory efficiency, which is why its base API is written
+around using as little as possible of it. This does make the API clumsier
+(requiring pre-order construction of all data, and making mutation harder).
+
+For times when efficiency is less important a more convenient object based API
+can be used (through `--gen-object-api`) that is able to unpack & pack a
+FlatBuffer into objects and standard TS types.
+
+**When using the obj based API, the flatbuffers import need to be in the global namespace if you don't have `--no-fb-import` enabled** since creating default values require accessing the `flatbuffers.js` file.
+
+To use:
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.ts}
+    // Autogenerated class from table Monster.
+    let monsterobj = new MonsterT();
+
+    // Deserialize from buffer into object.
+    Monster.getRootAsMonster(flatbuffer).unpackTo(monsterobj);
+    // or
+    let monsterobj = Monster.getRootAsMonster(flatbuffer).unpack();
+
+    // Update object directly like a regular TS class instance.
+    console.log(monsterobj.name);
+    monsterobj.name = "Bob";
+
+    // Serialize into new flatbuffer.
+    let fbb = new flatbuffers.Builder(1);
+    Monster.finishMonsterBuffer(fbb, monsterobj.pack(fbb));
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 ## Text parsing FlatBuffers in TypeScript
 
 There currently is no support for parsing text (Schema's and JSON) directly