(command.CommandList
  children: [
    (C {(Id.KW_Set set)} {(-ex)})
    (C {(source)} {($ Id.VSub_DollarName '$TRAVIS_BUILD_DIR') (/ci/travis_env_common.sh)})
    (C {(pushd)} {($ Id.VSub_DollarName '$ARROW_JS_DIR')})
    (C {(npm)} {(install)})
    (C {(popd)})
  ]
)