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Command Line Options

ckb-js-vm Command Line Options​

When an on-chain script is invoked by exec or spawn syscalls, it can accept command line arguments. The ckb-js-vm supports the following options to control its execution behavior:

  • -c <filename>: Compile JavaScript source code to bytecode, making it more efficient for on-chain execution
  • -e <code>: Execute JavaScript code directly from the command line string
  • -r <filename>: Read and execute JavaScript code from the specified file
  • -t <target>: Specify the target resource cell's code_hash and hash_type in hexadecimal format
  • -f: Enable file system mode, which provides support for JavaScript modules and imports

Note, the -c and -r options can only work with ckb-debugger. The -c option is particularly useful for preparing optimized bytecode as described in the previous section. When no options are specified, ckb-js-vm runs in its default mode. These command line options provide valuable debugging capabilities during development.

Compiling JavaScript into Bytecode​

The ckb-js-vm includes built-in functionality for compiling JavaScript code into bytecode, which improves execution efficiency on-chain. You can use this feature as follows:

ckb-debugger --read-file hello.js --bin build/ckb-js-vm -- -c hello.bc

This command:

  1. Uses --read-file hello.js to provide the JavaScript source file to ckb-debugger
  2. Specifies the ckb-js-vm binary with --bin build/ckb-js-vm
  3. Passes the -c hello.bc option to ckb-js-vm (everything after --)

The process compiles hello.js and outputs the bytecode to hello.bc. The --read-file option is specific to ckb-debugger and allows it to read a file as a data source. Command line arguments after the -- separator are passed directly to the on-chain script, enabling the use of the -c compilation flag.

Note that this compilation functionality requires the ckb-debugger environment and cannot work independently.

QuickJS bytecode is version-specific and not portable between different QuickJS versions. This compilation approach ensures that generated bytecode is always compatible with the exact QuickJS version used in ckb-js-vm.