Injecting Functions

During development, functions like loadScript are commonly used. Most projects will import the dependency @ckb-js-std/bindings. However, this module does not provide actual implementations of these functions — it's only intended for type checking and IDE code hints.

You can refer to Examples/call-syscalls, which contains a JS script that can be executed directly inside the JS-VM:

import { loadScript } from "@ckb-js-std/bindings";
console.log(loadScript);
console.log(new Uint8Array(loadScript(0, 8)));
console.log("End");

output:

Script log: Run from file, local access enabled. For Testing only.
Script log: function loadScript() {
    [native code]
}
Script log: 53,0,0,0,16,0,0,0
Script log: End
Run result: 0
All cycles: 3738804(3.6M)

In this example, @ckb-js-std/bindings is imported directly. Internally, this module is registered within the C code of the JS-VM using JS_NewCModule in qjs.c. The actual implementations are placed in ckb_module.c.

If developers have specific needs, they can inject custom functions in a similar way. However, we generally do not recommend this approach:

You would need to publish (i.e., deploy on-chain) the modified JS-VM, which consumes a significant amount of CKB and does not bring substantial performance benefits.
If you're modifying C code anyway, it's often better to use spawn or even exec as alternative solutions.

Injecting Functions​

Injecting Functions