javascript - In the js for in loop, using the push method of the array to obtain the properties of the object, the result is that the array is not changed

Question

Like the title
I don’t want to use jquery’s getOwnPropertyNames

var getProperty = function(obj) {
    var nArr = [];
    for (var i in obj) {
        nArr.push[i];
    }
    console.log(nArr);
    return nArr;
}
getProperty({a:1,b:2})

The final result returned is [];
if changed to

var getProperty = function(obj) {
    var nArr = [],
        k = 0;
    for (var i in obj) {
        nArr[k] = i;
        k++;
    }
    console.log(nArr);
    return nArr;
}
getProperty({a:1,b:2});

The correct result can be returned ['a','b'], why

Answer 1

nArr.push(i)
Wrong brackets! ! ! !

Answer 2

JS’s for in has a pitfall with hasOwnProperty.
You want to return ['a', 'b'], just:

Object.keys(obj)

That’s it (supports IE9+).

Answer 3

nArr.push[i]; Are you sure there will be no error when running this?