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Functions

Examples

This#

In order to call methods on cx.this, it must be downcasted to a JsObject. For more on type checking section for more details

pub fn require_object_this(mut cx: FunctionContext) -> JsResult<JsUndefined> {
let this = cx.this();
// Downcast `this` so .set can be called on it
let this = this.downcast::<JsObject>().or_throw(&mut cx)?;
let t = cx.boolean(true);
// Equivalent to `this.modified = true` in JS
this.set(&mut cx, "modified", t)?;
Ok(cx.undefined())
}

Calling JS Functions#

Here we define a JS function that takes a function as the 0th argument and calls that function. f.call takes a FunctionContext, the context to call the function from (in this case null), and arguments

pub fn call_js_function(mut cx: FunctionContext) -> JsResult<JsNumber> {
let f = cx.argument::<JsFunction>(0)?;
let args: Vec<Handle<JsNumber>> = vec![cx.number(16.0)];
let null = cx.null();
f.call(&mut cx, null, args)?.downcast::<JsNumber>().or_throw(&mut cx)
}

Constructing JS Functions#

pub fn construct_js_function(mut cx: FunctionContext) -> JsResult<JsNumber> {
let f = cx.argument::<JsFunction>(0)?;
let zero = cx.number(0.0);
let o = f.construct(&mut cx, vec![zero])?;
let get_utc_full_year_method = o.get(&mut cx, "getUTCFullYear")?.downcast::<JsFunction>().or_throw(&mut cx)?;
let args: Vec<Handle<JsValue>> = vec![];
get_utc_full_year_method.call(&mut cx, o.upcast::<JsValue>(), args)?.downcast::<JsNumber>().or_throw(&mut cx)
}

Returning Functions#

pub fn return_js_function(mut cx: FunctionContext) -> JsResult<JsFunction> {
JsFunction::new(&mut cx, add1)
}