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I'm looking at some code in an existing project and came across a js file containing one line: 

declare var __DEV__: boolean;

There is a syntax error that says:

Expected ; but found var

I tried removing the declare to change the line to: 

var __DEV__: boolean;

which gives the error:

Expected ; but found :

I've also read this post to understand how declarations work and confirm that it's necessary for this part of the code. I then compared the code to examples found here and couldn't pinpoint the mistake.

I considered changing the variable name, or declaring it differently, but I would like to understand how to do this correctly.

Code Maniac
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Manaar
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1 Answers1

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That's a Typescript construct. If you're writing vanilla JS, it doesn't apply.

In vanilla JS, just write

var __DEV__ = true; or var __DEV__ = false;

Jonathan Wilson
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  • I don't think removing/modifying the declaration is the correct approach. The user likely needs to understand that the project is not written in javascript, but needs to be transpiled to javascript. – Jake Holzinger Dec 07 '18 at 20:37
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    Agreed. I think that this is a yet another instance of the [XY problem](http://xyproblem.info/). – Jonathan Wilson Dec 07 '18 at 20:37