utilise/by.js

Lean JavaScript Utilities as Micro-libraries

var key = require('./key')
  , is  = require('./is')

module.exports = function by(k, v){
  var exists = arguments.length == 1
  return function(o){
    var d = is.fn(k) ? k(o) : key(k)(o)
    
    return d && v && d.toLowerCase && v.toLowerCase ? d.toLowerCase() === v.toLowerCase()
         : exists ? Boolean(d)
         : is.fn(v) ? v(d)
         : d == v
  }
}