Looping / iterating through an array of objects to return and array of strings - Javascript

Question

I've got an array of objects looking like this:

[{"key":"aaa","value":true},{"key":"bbb","value":false},{"key":"ccc","value":true}]

How can I iterate through it to get an array of?

["aaa", "bbb", "ccc"]

I am using node.js and this is the code. When I loop through it I get returned only the first "aaa" and I want to get a variable being an array of 3 objects?

router.get('/', function(req, res, next) {
    db.executeSql("SELECT this FROM that", function (data, err) {
        if (err) {       
            res.json(err);
        } 
        else {
            for (var i in data) {
                    for (var i=0; i < data.length; i++) {
                        var obj = data[i];
                        for (var property in obj) {
                            var a = (obj[property]);
                                res.json(a);
                                }
                    }
                }
            }   
        }   
        res.end();
    });
  });

If you could point me to the right direction or show me some examples, thanks!

intentionally-left-nil · Accepted Answer · 2016-02-17 22:12:16Z

5

var input = [{"key":"aaa","value":true},{"key":"bbb","value":false},{"key":"ccc","value":true}];

var output = input.map(function(datum){
    return datum.key;
});

returns an array of ["aaa", "bbb", "ccc"]

answered Feb 17, 2016 at 22:12

intentionally-left-nil

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3 Comments

Mac_W Over a year ago

after adding this code to else statement var output = data.map(function(datum){ return datum.key; }); res.json(output); it return [null,null]

intentionally-left-nil Over a year ago

I see that you have found out your issue below. In general, it is possible to run my above sample through your favorite javascript interpreter and see that output in this case does in fact equal ["aaa", "bbb", "ccc"]. So, there are a few possibilities here: Perhaps the inputs are wrong and they don't match. Perhaps how you are using the code snippet doesn't work. Or perhaps the caller is not getting the results properly. Adding debugging statements (console.log or otherwise) should generally help you further narrow down your issue.

Mac_W Over a year ago

you're right I've used a wrong query statement. Now I can see that map function is not mapping it just returns the whole array. I tested it somewhere else and it worked indeed. Do you think it can be related to mssql module which I am using or is it my mistake somewhere?

Ramya · Accepted Answer · 2016-02-17 22:48:39Z

0

var newArr = [];
var data = [{"key":"aaa","value":true},{"key":"bbb","value":false},{"key":"ccc","value":true}];
for(var i=0;i<data.length;i++){
    newArr.push(data[i].key);
}
return newArr;

answered Feb 17, 2016 at 22:48

Ramya

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