根据属性过滤对象数组

Question

The data I have stored is in a 2d Array.

One element of looks like below. (not an assignment operator)

someObjArray[5] === [{lastname:"foo", firstname:"bar", grade:10, userId:"foobar1234"},...]

For the particular above variable I want to filter on userId I am attempting to do so like this.

var test = stuArray[5].filter(function(item) {
    return item['userId'];
});

Resulting in:

test === [{lastname:"foo", firstname:"bar", grade:10, userId:"foobar1234"},...]

Where the desired results are

test === ["foobar1234",...]

I have also tried using a dot operator with the same results.

Answer 1

I don't think filter is what you're looking for here.

The function (non-anonymous in your case but you can also use anonymous functions) that you are passing into your filter method needs to return a true or a false. This is how the method "filters" your array - it gives you back an array whose elements pass the filter, or return true when passed as arguments into filter's function.

Note that this does not change the original array.

What you should use instead is the very similar map() function.

Note that map(), just like filter(), does not change the original array.

Answer 2

You can do it like this:

var someObjArray = [{lastname:"foo", firstname:"bar", grade:10, userId:"foobar1234"}];
console.log(someObjArray.map(s => s.userId));

Online demo (jsFiddle)