in content/references/java-chassis/en_US/search/lunr.js [319:330]
lunr.idf = function (posting, documentCount) {
var documentsWithTerm = 0
for (var fieldName in posting) {
if (fieldName == '_index') continue // Ignore the term index, its not a field
documentsWithTerm += Object.keys(posting[fieldName]).length
}
var x = (documentCount - documentsWithTerm + 0.5) / (documentsWithTerm + 0.5)
return Math.log(1 + Math.abs(x))
}