Warning: Reason support is experimental. We are looking for beta-tester and contributors.

Main Command-Line options

Option name Description
–version Display the version of the compiler
-o <file> Set the output filename to <file>
–source-map Generate sourcemap
–opt {1,2,3} Set the compilation profile (default 1). See Optimization section below.
–pretty Pretty print javascript output
–target-env Build javascript for the requested environment (default "isomorphic"). Isomorphic javascript runs in both the browser & nodejs. "nodejs" & "browser" options bundle less javascript, but drop support for APIs incompatible with the selected runtime.
–no-inline Disable code inlining
–debug-info Output debug information
-I dir Add <dir> to the list of include directories
–file file[:target] Register <file> to the pseudo filesystem and choose the destination <target>. The <target> can be a directory or a file (default /static/)
–enable <option> Enable option <option>
–disable <option> Disable option <option>


  • For Debugging: "–pretty –no-inline –debug-info" + eventually "–disable staticeval –disable share"
  • For Production: "–opt 3". It minimize the generated javascript by applying various optimizations until a fix-point is reached

List of option to "–disable" or "–enable"

Option name Default Description
pretty false Pretty print the javascript output
effects false Enable support for effect handlers
debuginfo false Output debug information (location)
deadcode true Deadcode elimination
globaldeadcode true Global deadcode elimination
inline true Code inlining
shortvar true Shorten variable names
staticeval true Static evaluation of constants
share true Share string and number constants
strict true Enable strict mode
debugger true Keep debugger statements. Stripped otherwise
genprim true Generate dummy primitives when missing
excwrap true Wrap js exception into ocaml ones
optcall true Javascript optimizations