docs.sheetjs.com/docz/docs/03-demos/12-engines/02_v8.md

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V8 is an embeddable JS engine written in C++. It powers Chromium and Chrome, NodeJS and Deno, Adobe UXP and other platforms.

The Standalone scripts can be parsed and evaluated in a V8 context.

Integration Details

Initialize V8

The official V8 hello-world example covers initialization and cleanup. For the purposes of this demo, the key variables are noted below:

v8::Isolate* isolate = v8::Isolate::New(create_params);
v8::Local<v8::Context> context = v8::Context::New(isolate);

The following helper function evaluates C strings as JS code:

v8::Local<v8::Value> eval_code(v8::Isolate *i, v8::Local<v8::Context> c, char* code) {
  v8::Local<v8::String> source = v8::String::NewFromUtf8(i, code).ToLocalChecked();
  v8::Local<v8::Script> script = v8::Script::Compile(i, source).ToLocalChecked();
  return script->Run(c).ToLocalChecked();
}

Load SheetJS Scripts

The main library can be loaded by reading the scripts from the file system and evaluating in the V8 context:

/* simple wrapper to read the entire script file */
static char *read_file(const char *filename, size_t *sz) {
  FILE *f = fopen(filename, "rb");
  if(!f) return NULL;
  long fsize; { fseek(f, 0, SEEK_END); fsize = ftell(f); fseek(f, 0, SEEK_SET); }
  char *buf = (char *)malloc(fsize * sizeof(char));
  *sz = fread((void *) buf, 1, fsize, f);
  fclose(f);
  return buf;
}

// ...
  size_t sz; char *file = read_file("xlsx.full.min.js", &sz);
  v8::Local<v8::Value> result = eval_code(isolate, context, file);

To confirm the library is loaded, XLSX.version can be inspected:

  /* get version string */
  v8::Local<v8::Value> result = eval_code(isolate, context, "XLSX.version");
  v8::String::Utf8Value vers(isolate, result);
  printf("SheetJS library version %s\n", *vers);

Reading Files

V8 supports ArrayBuffer natively. Assuming buf is a C byte array, with length len, this snippet stores the data as an ArrayBuffer in global scope:

/* load C char array and save to an ArrayBuffer */
std::unique_ptr<v8::BackingStore> back = v8::ArrayBuffer::NewBackingStore(isolate, len);
memcpy(back->Data(), buf, len);
v8::Local<v8::ArrayBuffer> ab = v8::ArrayBuffer::New(isolate, std::move(back));
v8::Maybe<bool> res = context->Global()->Set(context, v8::String::NewFromUtf8Literal(isolate, "buf"), ab);

/* parse with SheetJS */
v8::Local<v8::Value> result = eval_code(isolate, context, "globalThis.wb = XLSX.read(buf)");

wb will be a variable in the JS environment that can be inspected using the various SheetJS API functions.

Writing Files

The underlying memory from an ArrayBuffer can be recovered:

/* write with SheetJS using type: "array" */
v8::Local<v8::Value> result = eval_code(isolate, context, "XLSX.write(wb, {type:'array', bookType:'xlsb'})");

/* pull result back to C++ */
v8::Local<v8::ArrayBuffer> ab = v8::Local<v8::ArrayBuffer>::Cast(result);
size_t sz = ab->ByteLength();
char *buf = ab->Data();

The resulting buf can be written to file with fwrite.

Complete Example

:::note

This demo was tested in the following deployments:

V8 Version	Platform	OS Version	Compiler	Date
11.3.244.11	darwin-x64	macOS 13.2	clang 14.0.3	2023-05-20

:::

This program parses a file and prints CSV data from the first worksheet. It also generates an XLSB file and writes to the filesystem.

:::caution

At the time of writing, there were errors in the official V8 embed guide for the macOS platform. The correct instructions are included below.

:::

:::caution

The build process is long and will test your patience.

:::

Preparation

1. Download and install depot_tools:

mkdir -p /usr/local/lib
cd /usr/local/lib
git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git

2. Add the path to the PATH environment variable:

export PATH="/usr/local/lib/depot_tools:$PATH"

At this point, it is strongly recommended to add the line to a shell startup script such as .bashrc or .zshrc

3. Run gclient once to update depot_tools:

gclient

Clone V8

4. Create a base directory:

mkdir -p ~/dev/v8
cd ~/dev/v8
fetch v8
cd v8

Note that the actual repo will be placed in ~/dev/v8/v8.

5. Checkout the desired version. The following command pulls 11.3.244.11:

git checkout refs/tags/11.3.244.11 -b sample -t

Build V8

6. Build the static library.

tools/dev/v8gen.py x64.release.sample
ninja -C out.gn/x64.release.sample v8_monolith

7. Ensure the sample hello-world compiles and runs:

g++ -I. -Iinclude samples/hello-world.cc -o hello_world -fno-rtti -lv8_monolith \
    -lv8_libbase -lv8_libplatform -ldl -Lout.gn/x64.release.sample/obj/ -pthread \
    -std=c++17 -DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
./hello_world

Prepare Project

8. Make a new project folder:

cd ~/dev
mkdir sheetjs-v8
cd sheetjs-v8

9. Copy the sample source:

cp ~/dev/v8/v8/samples/hello-world.cc .

10. Create symbolic links to the include headers and obj library folders:

ln -s ~/dev/v8/v8/include
ln -s ~/dev/v8/v8/out.gn/x64.release.sample/obj

11. Build and run the hello-world example from this folder:

g++ -I. -Iinclude hello-world.cc -o hello_world -fno-rtti -lv8_monolith \
    -lv8_libbase -lv8_libplatform -ldl -Lobj/ -pthread -std=c++17 \
    -DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX
./hello_world

Add SheetJS

12. Download the standalone script and test file:

• xlsx.full.min.js
• pres.numbers

{\ curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js curl -LO https://sheetjs.com/pres.numbers}

13. Download sheetjs.v8.cc:

curl -LO https://docs.sheetjs.com/v8/sheetjs.v8.cc

14. Compile standalone sheetjs.v8 binary

g++ -I. -Iinclude sheetjs.v8.cc -o sheetjs.v8 -fno-rtti -lv8_monolith \
    -lv8_libbase -lv8_libplatform -ldl -Lobj/ -pthread -std=c++17 \
    -DV8_COMPRESS_POINTERS=1 -DV8_ENABLE_SANDBOX

15. Run the demo:

./sheetjs.v8 pres.numbers

If the program succeeded, the CSV contents will be printed to console and the file sheetjsw.xlsb will be created. That file can be opened with Excel.