Simple eample showing the usefulness of function composition in javascript

function_composition_example.js

function stringStartsWith(search, coll, prop, transform){
  return coll.filter(function(item){
    var key = transform ? transform(item[prop])  : item[prop];
    return key.indexOf(search) === 0
  });
}

function reverse(str){
  return str.split('').reverse().join('')
}

function lower (str){
  return str.toLowerCase()
}

var o = [
  {name: 'foo'},
  {name:'BAR'}
]

stringStartsWith('BAR', o,'name');          // FOUND
stringStartsWith('bar', o,'name', lower);   // FOUND
stringStartsWith('RAB', o,'name', reverse); // FOUND
stringStartsWith('bar', o,'name', reverse); // NOT FOUND

var lowerBack = _.compose(lower, reverse)

stringStartsWith('bar', o,'name', lowerBack); // FOUND