What steps can be taken to fix error TS2731 within this code snippet?

I've been working through a book and encountered an issue with the code below.

// This code defines a function called printProperty that has two generic type parameters
function printProperty<T, K extends keyof T>
 (object: T, key: K) {
 let propertyValue = object[key];
 console.log(`object[${key}] = ${propertyValue}`);
}

let obj1 = {
 id: 1,
 name: "myName",
 print() { console.log(`${this.id}`) }
}

printProperty(obj1, "id");
printProperty(obj1, "name");

The error message is:

index.ts(5,25): error TS2731: Implicit conversion of a 'symbol' to a 'string' will fail at runtime. Consider wrapping this expression in 'String(...)'.

I even tried disabling the strict option in the config file, but it didn't solve the problem.

Any suggestions or assistance would be greatly appreciated!

Answer №1

The types of keys within the object are as follows:

type PropertyKey = string | number | symbol;

As a result, keyof T encompasses symbol, and converting symbol to a string is considered invalid.

To improve your code, you can modify K to either include only string keys from T or both strings and numbers if necessary:

Only including string keys:

K extends keyof T & string

Including both string and number keys:

K extends keyof T & (string | number)

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