Can the typeof operator constantly display the changing data types assigned to a single variable?

Question

Can the typeof operator constantly display the changing data types assigned to a single variable?

Recently, I have been experimenting with the typeof operator in relation to the variables I am defining. In my Chrome developer console, I tried a statement that declared several variables like this:

var x, y, z;

Then, I proceeded to assign values to each variable like so:

var x = 7;
var y = 100;
var z = x + y;

Since it involved an arithmetic expression, when I used the typeof operator on each variable, it returned the string 'number'.

Curious about JavaScript quirks, I decided to play around some more and encountered something odd.

I then set each variable to undefined like this:

var x;

When I checked the type using the typeof operator on 'x', the result was unexpected.

typeof (x);

The output still showed as 'number'.

So, my question is: why does the typeof operator keep returning 'number' for an undefined variable in my example above?

javascript types operators literals

Answer 1

Answer №1

let y = 7;
let y;

That does not redeclare the variable. Variables cannot be truly redeclared. If you wish to change your variable to undefined, you can do so:

let y = 6;
y = undefined;
alert(typeof y);

Alternatively, you may want to delete it:

let context = {y:6};
delete context.y;
alert(typeof context.y);

However, this method does not work in the global ( window ) scope.

Answer 2

let y = 7;
let y;

That does not redeclare the variable. Variables cannot be truly redeclared. If you wish to change your variable to undefined, you can do so:

let y = 6;
y = undefined;
alert(typeof y);

Alternatively, you may want to delete it:

let context = {y:6};
delete context.y;
alert(typeof context.y);

However, this method does not work in the global ( window ) scope.

Answer 3

Answer №2

As illustrated in your scenario;

I made the decision to simply make each variable undefined like so.
var x;

Nevertheless, this action does not truly set x to undefined; instead, it essentially does nothing at all in practical terms.

The variable x will continue to hold the value you previously assigned to it (7).

If you explicitly define x as undefined (x = undefined), then its type will be accurately reflected by typeof (typeof x = "undefined").

Answer 4

As illustrated in your scenario;

I made the decision to simply make each variable undefined like so.
var x;

Nevertheless, this action does not truly set x to undefined; instead, it essentially does nothing at all in practical terms.

The variable x will continue to hold the value you previously assigned to it (7).

If you explicitly define x as undefined (x = undefined), then its type will be accurately reflected by typeof (typeof x = "undefined").

Answer 5

Answer №3

Variables are initialized only once and then reused in subsequent operations.

var x = 1;
...
x = 2;
...
x = undefined;

If a variable is created again, the computer will prioritize the one with data already assigned to it.

var x = 1;
var x = 2;//this
...
var y = 1;//this
var y;

Answer 6

Variables are initialized only once and then reused in subsequent operations.

var x = 1;
...
x = 2;
...
x = undefined;

If a variable is created again, the computer will prioritize the one with data already assigned to it.

var x = 1;
var x = 2;//this
...
var y = 1;//this
var y;

Can the typeof operator constantly display the changing data types assigned to a single variable?

Answer №1

Answer №2

Answer №3

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