index.js
function packageFilter(pkg, root) {
  pkg.main = pkg.glslify || (
    path.extname(pkg.main || '') !== '.js' &&
    pkg.main
  ) || 'index.glsl'

  return pkg
}
function packageFilter(pkg, root) {
  pkg.main = pkg.glslify || (
    path.extname(pkg.main || '') !== '.js' &&
    pkg.main
  ) || 'index.glsl'

  return pkg
}
function packageFilter ( pkg , root ) { pkg . main = pkg . glslify || ( path . extname ( pkg . main || '' ) !== '.js' && pkg . main ) || 'index.glsl' return pkg }
find the "glslify", "main", or assume main == "index.glsl" if main is a .js file then ignore it.
find the glslify main or assume main == index . glsl if main is a . js file then ignore it .