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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def build_js(ctx, force=False):
 """Build all javascript files. """

    for fname in JSX_FILENAMES:
        jstools.babel(
            ctx,
            '{pkg.source_js}/' + fname,
            '{pkg.django_static}/{pkg.name}/js/' + fname + '.js',
            force=force
        )