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# Variadic Parameters
In javascript, both the types of function arguments, and the number of function arguments are
dynamic. For example
```js
function sum(...rest) {
let i;
// the old way
let old_way = 0;
for (i=0; i<arguments.length; i++) {
old_way += arguments[i];
}
// the new way
let new_way = 0;
for (i=0; i<rest.length; i++) {
new_way += rest[i];
}
// both give the same answer
assert(old_way === new_way);
return new_way;
}
```
This function doesn't translate directly into rust, since we don't currently support variadic
arguments on the wasm target. To bind to it, we use a slice as the last argument, and annotate the
function as variadic:
```rust
#[wasm_bindgen]
extern "C" {
#[wasm_bindgen(variadic)]
fn sum(args: &[i32]) -> i32;
}
```
when we call this function, the last argument will be expanded as the javascript expects.
To export a rust function to javascript with a variadic argument, we will use the same bindgen variadic attribute and assume that the last argument will be the variadic array. For example the following rust function:
```rust
#[wasm_bindgen(variadic)]
pub fn variadic_function(arr: &JsValue) -> JsValue {
arr.into()
}
```
will generate the following TS interface
```ts
export function variadic_function(...arr: any): any;
```
Version data entries
30 entries across 30 versions & 1 rubygems