Typescript force Check property in object when treated as associative array

Question

Better explain with example let's say I have :

class Model{
    property1: number;
    property2: number;
}

let model= new Model;

When I do

model["property1"]="sdaef" // Good ! typescript checks and know it should be number and give error

var test = model.nonExistingProp // throws error since the property does not exist which is good

Now the problem

    var test = model["nonExistingProp"]; // NO ERRORS ??

I'm wondering since it is smart enough to know the properties from strings (associative array) and their types why does not throw error like previous example and say nonExistingProp, is there a way to force this kind of type checking on associative array since it already knows the properties and did the check for the type like first example ??

Thanks

Daniel Rosenwasser · Accepted Answer · 2017-06-07 16:25:06Z

1

TypeScript is smart enough, but this is a legacy feature for when indexing into an object was used as a form of getting around the type-checker.

However, if you use --noImplicitAny (in addition to the other --strict flags), you'll get safer checking and TypeScript will give an error on that expression.

For the record, flags the team has placed under the --strict flag are things that the team believes will give you a much better experience in editing & error checking.

answered Jun 7, 2017 at 16:25

Daniel Rosenwasser

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2 Comments

Ahmed Over a year ago

by the way can i force strict check only for that file ?

Ahmed Over a year ago

i thought there might be something like ts-check flag that's added to js files that can be applied locally

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