How to combine object array values into 1 array?

Question

I have a data object with each object containing a tags array, I would like to loop through the object and grab each of the object tags and combine eventually combine the values into 1 array called selections on completion of the loop. At the moment however I'm unable to solve this, I have tried pushing the tags into an array then use the underscore _.union method and also tries concatenating each looped array into 1 but with no success. Can anyone recommend a solution?

Fiddle: http://jsfiddle.net/24qh7zfv/3/

JS

var selection = [];
var data = ([
 {
 role: "Developer",
 tag: "developer",
 tags: ["Javascript", "CSS", "HTML"] 
 }, {
 role: "Producer",
 tag: "producer",
 tags: ["Project Management", "Pitching", "Billing"] 
 }
]);
for( var i = 0, len = data.length; i < len; i++ ) {
 selection.concat(data[i].tags);
}
console.log(selection);

Answer 1

You need to reassign selection, and concat to tho that. so use:

for( var i = 0, len = data.length; i < len; i++ ) {
 selection = selection.concat(data[i].tags);
}

Answer 2

This should work.

var selection = [];
var data = [
 {
 role: "Developer",
 tag: "developer",
 tags: ["Javascript", "CSS", "HTML"] 
 }, {
 role: "Producer",
 tag: "producer",
 tags: ["Project Management", "Pitching", "Billing"] 
 }
];
for( var i = 0; i < data.length; i++ ) {
 for(var j = 0; j < data[i].tags.length; j++){
 selection.push(data[i].tags[j]);
 }
}

Answer 3

You can simply do this.

var selection = data.map(function(x){
 return x.tags;
}).join().split(",");

Answer 4

i think better use concat array function . see concat function in http://skillgun.com/javascript/arrays/tutorial