microsoft / microsoft/TypeScript

No validation in JSX when using template string index signatures

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#44,797 11 comments 0 reactions 1 assignee View on GitHub

@ahejlsberg is already working on this.

Since Jun 29, 2021.

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Description

Playground Link

Here's the shortest example:

import * as React from "react";

interface Props {
    foo: string;
    bar: number;
    [dataProp: `data-${string}`]: string;
}

function Yadda(props: Props) {
    return <div />;
}

let props: Props = {
    foo: "",
    bar: 0,
    "data-yadda": 42,
};

let x = <Yadda foo="hello" bar={42} data-yadda={42} />;

Expected: TypeScript should error on data-yadda, just as if we had explicitly declared a data-yadda property in Props, or if we had used a string index signature.
Actual: JSX dashed properties are exempt from these checks on the target object if a corresponding property doesn't exist.

My expectation is that if an index signature exists, and a property should be covered by that index signature, then TypeScript should check that the property is compatible with that index signature.

Here's a longer example that could be used in tests.

import * as React from "react";

interface Props {
    foo: string;
    bar: number;
    [dataProp: `data-${string}`]: string;
}

function Yadda(props: Props) {
    return <div />;
}

// Errors as expected on data-yadda. ✅
let propsObj1: Props = {
    foo: "",
    bar: 0,
    "data-yadda": 42,
};

// Should error on data-yadda, does not. ❌
let x = <Yadda foo="hello" bar={42} data-yadda={42} />;

/////////

let propsObj2 = {
    foo: "",
    bar: 0,
    "data-yadda": 42,
};

// Should error on data-yadda, does not. ❌
let y = <Yadda {...propsObj2} />

// Errors as expected on data-yadda. ✅
propsObj1 = propsObj2;

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