I am quite confused when should we declare object inside an array / array inside an object.
Object inside an array
var data = [{'Name': Alex,'Value': 2}]
Array inside an object
var data = {interest:['a','b','c'], name:['Ali','Baba','Alan']}
Can anyone help to explain this? thanks in advance
Both representations are valid, but you should choose one according to what you are doing with this data afterwards. You should ask yourself: What kind of operations are more frequent: add/delete or read/find? The answer to this question may help you to choose.
With array of objects it is easier to add/delete entities, which may be done as single atomic action. Consider the following case:
var arr = [{x: 'a', y: 1}, {x: 'b', y: 2}];
arr.push({x: 'c', y: 3}); // add new to the end
var obj = arr.shift(); // remove first element of array and assign it to variable
With Object of arrays you will need to remove x and y separately:
var obj = {x: ['a', 'b'], y: [1, 2]};
// add
obj.x.push('c');
obj.y.push(3);
// remove
obj.x.shift();
obj.y.shift();
However, when you have a lot of empty values, object of arrays may have more compact representation (read: less bites to send over network) and less iterations to find something (like min/max).
var arr = [
{x: 'a'},
{y: 1},
{y: 2},
{y: 3},
{y: 4},
{y: 5},
{x: 'b', y: 6}
];
// Find max of x
var maxX = arr.reduce(function(max, obj) { // 7 iterations
return obj.x > max ? obj.x : max;
}, '')
The same with object of arrays:
// more compact
var obj = {
x: ['a', 'b'],
y: [1, 2, 3, 4, 5, 6]
}
// less iterations (only 2 in this case)
var maxX = obj.x.reduce(function(max, val) {
return val > max ? val : max;
}, '')
[{name: 'foo'}, {name: 'bar'}]is not really a good idea because looking for an object in the array is O(n) and you don't need order herewhen to use bulletpoints in a table instead of table under bulletpoints