I have an object array and I want to create a new array with the ids only. Some records have id and others don't.
So I have something like:
var myMap = arr.map(function(e) {
return e.id;
});
console.log(myMap); // [undefined, 2, 3, 4]
I'd like it to return just [2, 3, 4], if possible.
This JSFiddle should explain a little better: http://jsfiddle.net/dmathisen/Lnmj0w8k/
It's not possible with just Array.map, you have to filter as well.
var myMap = arr.map(function(e) {
return e.id;
}).filter(function(x) {
return typeof x !== 'undefined';
});
As the ID's are always strings, you can do it like this as well
var myMap = arr.map(function(e) {
return 'id' in e ? e.id : false;
}).filter(Boolean);
var myMap = arr.filter(function(e) {
return e.hasOwnProperty("id")
}).map(function(e) {
return e.hasOwnProperty("id") ? e.id : null;
});
As others have said, if you stick to pure jQuery your only option is to combine your map with a filter, or otherwise post-process the map results yourself.
However, if you combine jQuery with the popular Underscore.js library, the problem becomes trivial thanks to Underscore's compact method:
var myMap = arr.map(function(e) {
return e.id;
});
myMap = _(myMap).compact();
But if you use Underscore, there's an even simpler way to do the same thing, because Underscore has a method specifically for extracting a certain property from an object:
var myMap = _(arr).pluck('id');
myMap = _(myMap).compact();
You can even chain the two together:
var myMap = _(arr).chain().pluck('id').compact().value();
or you can throw in the Underscore Grease library to get what I consider to be the simplest possible solution:
var myMap = _(arr).pluck_('id').compact();
