Question

This question is about JavaScript language fundamentals. Why we can use dot (.) operator to access an object’s elements but not for array elements?

In other words why myArray.0 is not valid in JavaScript?

Answer 1

A javascript property name accessed with the dot notation cannot start with a number. That’s just part of the javascript syntax rules/grammar. So, even if dot notation could work for arrays, it won’t because array indexes are numbers and property names that start with numbers cannot be accessed with dot notation.

For arrays, you can obviously use:

myArray[0]

But, that also works for object properties that start with a number like:

var x = {"12": "foo"};
alert(x["12"]);     // foo

And, you cannot do:

alert(x.12)

even when x is an object and "12" is a legitimate property on the object. You would have to use x["12"] to access it.