---
title: C + QuickJS
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---
QuickJS is an embeddable JS engine written in C. It provides a separate set of
functions for interacting with the filesystem and the global object. It can run
the standalone browser scripts.
The [Standalone scripts](/docs/getting-started/installation/standalone) can be
parsed and evaluated in a QuickJS context.
## Integration Details
_Initialize QuickJS_
QuickJS provides a `global` object through `JS_GetGlobalObject`:
```c
/* initialize */
JSRuntime *rt = JS_NewRuntime();
JSContext *ctx = JS_NewContext(rt);
/* obtain reference to global object */
JSValue global = JS_GetGlobalObject(ctx);
/* DO WORK HERE */
/* free after use */
JS_FreeValue(ctx, global);
/* cleanup */
JS_FreeContext(ctx);
JS_FreeRuntime(rt);
```
:::warning
All values must be freed with `JS_FreeValue` before calling `JS_FreeContext`!
`JS_IsException` should be used for validation.
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 QuickJS context:
```c
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); fsee (f, 0, SEEK_SET); }
char *buf = (char *)malloc(fsize * sizeof(char));
*sz = fread((void *) buf, 1, fsize, f);
fclose(f);
return buf;
}
// ...
/* load library */
{
size_t len; char *buf = read_file("xlsx.full.min.js", &len);
JS_Eval(ctx, buf, len, "", 0);
free(buf);
}
```
To confirm the library is loaded, `XLSX.version` can be inspected:
```c
/* obtain reference to the XLSX object */
JSValue XLSX = JS_GetPropertyStr(ctx, global, "XLSX");
/* print version */
JSValue version = JS_GetPropertyStr(ctx, XLSX, "version");
size_t vlen; const char *vers = JS_ToCStringLen(ctx, &vlen, version);
printf("Version: %s\n", vers);
```
### Reading Files
`JS_NewArrayBuffer` can generate an `ArrayBuffer` from a C byte array. The
function signature expects `uint8_t *` instead of `char *`:
```c
/* read file */
size_t dlen; uint8_t * dbuf = (uint8_t *)read_file("pres.numbers", &dlen);
/* load data into array buffer */
JSValue ab = JS_NewArrayBuffer(ctx, dbuf, dlen, NULL, NULL, 0);
/* obtain reference to the XLSX object */
JSValue XLSX = JS_GetPropertyStr(ctx, global, "XLSX");
/* call XLSX.read(ab) */
JSValue XLSX_read = JS_GetPropertyStr(ctx, XLSX, "read");
JSValue args[] = { ab };
JSValue wb = JS_Call(ctx, XLSX_read, XLSX, 1, args);
```
## Complete Example
The "Integration Example" covers a traditional integration in a C application,
while the "CLI Test" demonstrates other concepts using the `quickjs` CLI tool.
### Integration Example
:::note
This demo was last tested on 2023 March 11 against QuickJS commit `2788d71` 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 `libquickjs.a`:
```bash
git clone --depth=1 https://github.com/bellard/quickjs
cd quickjs
git checkout 2788d71
make
cd ..
```
1) Copy `libquickjs.a` and `quickjs.h` into the working directory:
```bash
cp quickjs/libquickjs.a .
cp quickjs/quickjs.h .
```
2) Download [`sheetjs.quick.c`](pathname:///quickjs/sheetjs.quick.c):
```bash
curl -LO https://docs.sheetjs.com/quickjs/sheetjs.quick.c
```
3) Build the sample application:
```bash
gcc -o sheetjs.quick -Wall -lm libquickjs.a sheetjs.quick.c
```
This program tries to parse the file specified by the first argument
4) Download the standalone script and test file:
```bash
curl -LO https://cdn.sheetjs.com/xlsx-latest/package/dist/xlsx.full.min.js
curl -LO https://sheetjs.com/pres.numbers
```
5) Run the test program:
```
./sheetjs.quick pres.numbers
```
If successful, the program will print the library version number, file size,
first worksheet name, and the contents of the first sheet as CSV rows.
### CLI Test
:::note
This demo was last tested on 2023 March 11 against QuickJS `2021-03-27`.
:::
0) Ensure `quickjs` command line utility is installed
1) Download the standalone script and the test file: