From vanilla JavaScript to the powerful lodash library

Can you help me determine if these statements are equivalent?

myApp.filter('myFilter', function() {

  var result, i, sport, y, contains, league;
  return function(sports, filterBy) {    
    if (angular.isUndefined(sports) || !filterBy) {
      return sports;
    }

    filterBy = filterBy.toLowerCase();
    result = [],
    contains = function(haystack, needle) {
      return haystack.toLowerCase().indexOf(needle) > -1;
    };

    for (i = 0; i < sports.length; i++) {
      sport = sports[i];
      if (contains(sport.name, filterBy)) {
        result.push(sport);
        continue;
      } else {
        for (y = 0; y < sport.leagues.length; y++) {
          league = sport.leagues[y];
          if (contains(league.name, filterBy)) {
            result.push(sport);
            break;
          }
        }
      }
    }
    return result;
  };
});

Using lodash:

myApp.filter('myFilter', function() {

  var result, i, sport, y, contains, league;
  return function(sports, filterBy) {    
    if (angular.isUndefined(sports) || !filterBy) {
      return sports;
    }

    filterBy = filterBy.toLowerCase();
    result = [],
    contains = function(haystack, needle) {
      return haystack.toLowerCase().indexOf(needle) > -1;
    };

  _.each(sports.length, function(sport) {
      if (contains(sport.name, filterBy)) {
        result.push(sport);
        continue;
      } else {
        _.each(sport.leagues.length, function(league) {
          if(contains(league.name, filterBy)) {
            result.push(sport);
            break;
          }
        });
      }
    });

I'm trying to understand the logic behind using lodash. I have the same function in pure JavaScript, but when I try to convert it to lodash, my app stops working. Can you help me identify where I might be going wrong? You can check out the Plnkr with the pure JavaScript function in the library section where I've used underscore instead of lodash since lodash didn't load properly. My goal is to translate the function into a lodash function using _.each instead of a traditional for loop.

javascriptangularjsunderscore.jslodash

Answer №1

To handle this scenario, the use of "each" is not recommended. Additionally, with "each" you do not have the ability to "continue" or "break". In my opinion, utilizing "filter" would be more appropriate for obtaining a filtered result. Here is how the code should be structured:

var result = sports.filter(function(sport){
  return (
      contains(sport.name, filterBy) 
    || (
      sport.leagues && sport.leagues.some(function(league) { 
        return contains(league.name, filterBy) 
      })
    )
  )
})

Alternatively, for lodash/underscore:

var result = _.filter(sports, function(sport) {
  return (
      contains(sport.name, filterBy) 
    || (
      sport.leagues && _.some(sport.leagues, function(league) { 
        return contains(league.name, filterBy);
      })
    )
  )
});

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