Cannot redeclare block-scoped variable 'name' In TypeScript

Question

Hi I am learning typescript.

I have in my code.

var name:string="Hello world";
console.log(name);

while compile time I am getting this error.

error TS2451: Cannot redeclare block-scoped variable 'name'.
index.ts(4,5): error TS2451: Cannot redeclare block-scoped variable 'name'.

Can someone describe me why I am getting this error?

The error seems to suggest that you've already got a variable called name in scope. — phuzi
– phuzi, Commented Nov 28, 2017 at 14:37

Nitzan Tomer · Accepted Answer · 2017-11-28 14:58:59Z

21

The name property is defined on the window object:

interface Window extends EventTarget, WindowTimers, WindowSessionStorage, WindowLocalStorage, WindowConsole, GlobalEventHandlers, IDBEnvironment, WindowBase64, GlobalFetch {
    ...
    name: string;
    ...
}

(https://github.com/Microsoft/TypeScript/blob/master/lib/lib.d.ts#L17226)

You'll need to come up with a new name for your variable:

var myname = "Hello world";
console.log(myname);

edited Nov 28, 2017 at 14:58

answered Nov 28, 2017 at 14:40

Nitzan Tomer

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Comments

ColdFire · Accepted Answer · 2019-02-16 06:45:54Z

13

You can add export{} at the beginning of your file.

answered Feb 16, 2019 at 6:45

ColdFire

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2 Comments

rahul Over a year ago

Could you explain a bit why to do so.

heretoinfinity Over a year ago

@rahul, the export {} makes it a module and so it has its own module scope and can thus use name without a class. See medium.com/@muravitskiy.mail/…

Pac0 · Accepted Answer · 2017-11-28 14:37:57Z

2

Your variable name has already been declared somewhere in the same block of code. And it is not allowed.

This is exactly the meaning of the error message.

The cause being that, you tried to declare this particular variable on global scope, and here name is already defined for some technical reason, for more details see : https://github.com/Microsoft/TypeScript/issues/9850

(Thanks @betadeveloper )

edited Nov 28, 2017 at 14:37

answered Nov 28, 2017 at 14:30

Pac0

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3 Comments

user8928802 Over a year ago

No. It is a global in the browser - window.name and in typescript they decided to declare it as a const, see this issue github.com/Microsoft/TypeScript/issues/9850

Pac0 Over a year ago

Thank you for the insight, I edited my answer adding the cause on this specific case.

Paaarth Over a year ago

@Pac0 Thanx Brother :-)

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