Underscore.js _.map function : skip a value

Question

I am trying to use underscore.js _.map function on an array of objects, to get an array with a property of each object. That's the usual scenario, so :

var finalArray = _.map(myArray, function(obj) {     return obj.myProperty; }); 

But in some cases I need that nothing be added in the array. It could be something like :

var finalArray = _.map(myArray, function(obj) {     if (!obj.ignore) {         return obj.myProperty;     } }); 

The result of this is that an undefined value is pushed into the array, which is not the same as not pushing anything at all.

Is there a way for the map function not to push a value, or do I need to post-process my finalArray to remove the unwanted undefined's?

Answer 1

you should use _.filter() before _.map()

var filteredArray = _.filter(myArray,function(obj) {      return !obj.ignore; });  var finalArray = _.map(filteredArray, function(obj) {     return obj.myProperty; }); 

Answer 2

You could use reduce:

myArray.reduce(function (acc, obj) {     if (!obj.ignore) {         acc.push(obj.myProperty);     }     return acc; }, []); 

or with lodash:

_.reduce(myArray, function (acc, obj) {   if (!obj.ignore) {     acc.push(obj.myProperty);   }   return acc; }, []);