typescript: detect assignment to un-initialized variable at compile time

Question

Please see the code here

interface ITest {
    Name: string
}

var t:ITest;
//var t:ITest = {Name:null};

t.Name = "hello";

this is a runtime error as t never initialized, and can solve by uncommenting the line. Is there a way to detect assignment to un-initialized variable at compile time?

WiredPrairie · Accepted Answer · 2014-03-19 19:09:15Z

1

No, there isn't a standardized way in TypeScript to prevent assignment to a property of an un-initialized variable.

Many would try to catch that error through a unit test or an assertion library that would verify the object exists before setting the property.

answered Mar 19, 2014 at 19:09

WiredPrairie

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basarat · Accepted Answer · 2014-03-19 22:33:05Z

1

No TS can't do that. For good reason. Say you declare in file a, setup in file b and use in file c.

TypeScript can't know that you are going to load file a then b then c. At runtime you might end up loading files c first (using a script tag) and will still get this error.

answered Mar 19, 2014 at 22:33

basarat

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1 Comment

WiredPrairie Over a year ago

While it's true that there are cases where it couldn't work, there certainly are cases where it could.

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