docs.sheetjs.com/docz/docs/03-demos/12-engines/20_chakra.md

---
title: C++ + ChakraCore
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---

import current from '/version.js';
import CodeBlock from '@theme/CodeBlock';

ChakraCore is an embeddable JS engine written in C++.

The [Standalone scripts](/docs/getting-started/installation/standalone) can be
parsed and evaluated in a ChakraCore context.

## Integration Details

_Initialize ChakraCore_

ChakraCore provides a `global` object through `JsGetGlobalObject`:

```cpp
/* initialize */
JsRuntimeHandle runtime;
JsContextRef context;
size_t cookie = 0;
JsCreateRuntime(JsRuntimeAttributeNone, nullptr, &runtime);
JsCreateContext(runtime, &context);
JsSetCurrentContext(context);

/* obtain reference to global object */
JsValueRef global;
JsGetGlobalObject(&global);

/* DO WORK HERE */

/* cleanup */
JsSetCurrentContext(JS_INVALID_REFERENCE);
JsDisposeRuntime(runtime);
```

:::note

Cleanup and validation code is omitted from the discussion.  The integration
example shows structured validation and controlled memory usage.

:::

_Load SheetJS Scripts_

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

```cpp
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;
}

#define EVAL_FILE(path) {\
  JsValueRef filename; \
  JsValueRef result; \
  JsCreateString(path, strlen(path), &filename); \
  size_t len; const char* script = read_file(path, &len);\
  JsValueRef src;\
  JsCreateExternalArrayBuffer((void*)script, len, nullptr, nullptr, &src);\
  JsRun(src, cookie++, filename, JsParseScriptAttributeNone, &result); \
}

// ...
  /* load library */
  EVAL_FILE("shim.min.js")
  EVAL_FILE("xlsx.full.min.js")
```

### Reading Files

`JsCreateExternalArrayBuffer` can generate an `ArrayBuffer` from a C byte array:

```cpp
/* read file */
size_t len; char *buf = read_file(argv[1], &len);

/* load data into array buffer */
JsValueRef ab;
JsCreateExternalArrayBuffer((void*)buf, len, nullptr, nullptr, &ab);
```

After pushing the data, it is easiest to store properties on `globalThis`:

```cpp
/* assign to the `buf` global variable */
JsValueRef buf_str; JsCreateString("buf", strlen("buf"), &buf_str);
JsObjectSetProperty(global, buf_str, ab, true);

/* call globalThis.wb = XLSX.read(ab) */
const char* script_str ="globalThis.wb = XLSX.read(buf);"

JsValueRef script;
JsCreateExternalArrayBuffer((void*)script_str, (size_t)strlen(script_str), nullptr, nullptr, &script);
JsRun(script, cookie++, fname, JsParseScriptAttributeNone, &result);
```

## Complete Example

The "Integration Example" covers a traditional integration in a C application,
while the "CLI Test" demonstrates other concepts using the `ch` CLI tool.

### Integration Example

:::note

This demo was last tested on 2023 April 09 against ChakraCore commit `c3ead3f`
on a Intel Mac. `gcc -v` printed:

```
Apple clang version 14.0.0 (clang-1400.0.29.202)
Target: x86_64-apple-darwin21.6.0
```

:::

0) Build ChakraCore:

```bash
git clone https://github.com/Microsoft/ChakraCore
cd ChakraCore
git checkout c3ead3f
./build.sh --static --icu=/usr/local/opt/icu4c/include --test-build -j=8
cd ..
```

1) Download the source file and `Makefile`:

- [`sheetjs.ch.cpp`](pathname:///chakra/sheetjs.ch.cpp)
- [`Makefile`](pathname:///chakra/Makefile)

```bash
curl -LO https://docs.sheetjs.com/chakra/sheetjs.ch.c
curl -LO https://docs.sheetjs.com/chakra/Makefile
```

2) Build the sample application:

```bash
make
```

This program tries to parse the file specified by the first argument

4) Download the standalone script, shim script, and test file:

<ul>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}>xlsx.full.min.js</a></li>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js`}>shim.min.js</a></li>
<li><a href="https://sheetjs.com/pres.numbers">pres.numbers</a></li>
</ul>

<CodeBlock language="bash">{`\
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js
curl -LO https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js
curl -LO https://sheetjs.com/pres.numbers`}
</CodeBlock>

5) Run the test program:

```
./sheetjs.ch pres.numbers
```

If successful, the program will print the contents of the first sheet as CSV.


### CLI Test

:::note

This demo was last tested on 2023 April 09 against `ch` `1.13.0.0-beta`.
The command line tool was built against commit `c3ead3f`.

:::

Due to limitations of the `ch` standalone binary, this demo will encode a test
file as a Base64 string and directly add it to an amalgamated script.

0) Download and extract the ChakraCore release ZIP.  Copy the binary (`bin/ch`)
to your project folder.

1) Download the standalone script, shim, and test file:

<ul>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/xlsx.full.min.js`}>xlsx.full.min.js</a></li>
<li><a href={`https://cdn.sheetjs.com/xlsx-${current}/package/dist/shim.min.js`}>shim.min.js</a></li>
<li><a href="https://sheetjs.com/pres.numbers">pres.numbers</a></li>
</ul>

2) Bundle the test file and create `payload.js`:

```bash
node -e "fs.writeFileSync('payload.js', 'var payload = \"' + fs.readFileSync('pres.numbers').toString('base64') + '\";')"
```

3) Create support scripts:

- `global.js` creates a `global` variable:

```js title="global.js"
var global = (function(){ return this; }).call(null);
```

- `chakra.js` will call `XLSX.read` and `XLSX.utils.sheet_to_csv`:

```js title="chakra.js"
var wb = XLSX.read(payload, {type:'base64'});
console.log(XLSX.utils.sheet_to_csv(wb.Sheets[wb.SheetNames[0]]));
```

4) Create the amalgamation `xlsx.chakra.js`:

```bash
cat global.js xlsx.full.min.js payload.js chakra.js > xlsx.chakra.js
```

The final script defines `global` before loading the standalone library.  Once
ready, it will read the bundled test data and print the contents as CSV.

5) Run the script using the ChakraCore standalone binary:

```
./ch xlsx.chakra.js
```