You have to use bracket notation:

var obj = {};
obj[a[i]] = 0;
x.push(obj);

The result will be:

x = [{left: 0}, {top: 0}];

Maybe instead of an array of objects, you just want one object with two properties:

var x = {};

and

x[a[i]] = 0;

This will result in x = {left: 0, top: 0}.

Maybe you would be better of using an object,

So you could do

var d  = {
"Label" : "Value"
};

And to add the value you could

d.label = "value";

This might be a more structured approach and easier to understand if your arrays become big. And if you build the JSON valid it's easy to make a string and parse it back in.

Like var stringD = JSON.stringify(d); var parseD = JSON.parse(stringD);

UPDATE - ARRAY 2D

This is how you could declare it

var items = [[1,2],[3,4],[5,6]];

alert(items[0][0]);

And the alert is reading from it,

To add things to it you would say items[0][0] = "Label" ; items[0][1] = "Value";

If you want to do all the labels then all the values do...

for(var i = 0 ; i < labelssize; i ++)
{
  items[i][0] = labelhere;
}


for(var i = 0 ; i < labelssize; i ++)
{
  items[i][1] = valuehere;
}

There are no keys in JavaScript arrays. Use objects for that purpose.

var obj = {};

$.getJSON("displayjson.php",function (data) {
    $.each(data.news, function (i, news) {
        obj[news.title] = news.link;
    });                      
});

// later:
$.each(obj, function (index, value) {
    alert( index + ' : ' + value );
});

In JavaScript, objects fulfill the role of associative arrays. Be aware that objects do not have a defined "sort order" when iterating them (see below).

However, In your case it is not really clear to me why you transfer data from the original object (data.news) at all. Why do you not simply pass a reference to that object around?

You can combine objects and arrays to achieve predictable iteration and key/value behavior:

var arr = [];

$.getJSON("displayjson.php",function (data) {
    $.each(data.news, function (i, news) {
        arr.push({
            title: news.title, 
            link:  news.link
        });
    });                      
});

// later:
$.each(arr, function (index, value) {
    alert( value.title + ' : ' + value.link );
});

var items = [{
    'id1': 1,
    'id2': 2,
    'id3': 3,
    'id4': 4
}];

// items[0] is an object
items[0].id5= 5;
console.log(items)

Use .push:

items.push({'id':5});

var arr = [];

for (var prop in obj) {
   if (obj.hasOwnProperty(prop)) {
      var innerObj = {};
      innerObj[prop] = obj[prop];
      arr.push(innerObj)
   }
}
    
console.log(arr);

here is demo https://plnkr.co/edit/9PxisCVrhxlurHJYyeIB?p=preview

const data = [{"label": "a", "value": 4}, {"label": "b", "value": 1}, {"label": "c", "value": 2}];
const out = data.map((item, index) => [index + 1, item.value]);
console.log(out);