The type undefined cannot be assigned to the type even with a null check

Question

The type undefined cannot be assigned to the type even with a null check

When looking at my code, I encounter an error stating

Argument of type 'Definition | undefined' is not assignable to parameter of type 'Definition'

. Even though I am checking if the object value is not undefined with if (defs[type] != undefined), the error persists at

this.addDefinition(type, defs[type])

.

public static addDefinitions(defs: Record<string, Definition>): void {
        Object.keys(defs).forEach((type: string): void => {
            if (defs[type] != undefined) {
                this.addDefinition(type, defs[type]);
            }
        });
    }

Could there possibly be a misconfiguration in my tsconfig causing this issue?

typescript

Answer 1

Answer №1

I would love to provide a more detailed response, but here is the possible solution TS might be anticipating in relation to a basic Record<string,T> object. (Please note that this is just my educated guess: It seems like TS may not remember 'type' as a specific string and could potentially overlook checking that key even within the same process.)

    public static addDefinitions(defs: Record<string, Definition>): void {
        Object.keys(defs).forEach((type: string): void => {
            const def = defs[type] // assigning value to a variable

            if (def) {
                this.addDefinition(type, def); // validating def
            }
        });
    }

Answer 2

I would love to provide a more detailed response, but here is the possible solution TS might be anticipating in relation to a basic Record<string,T> object. (Please note that this is just my educated guess: It seems like TS may not remember 'type' as a specific string and could potentially overlook checking that key even within the same process.)

    public static addDefinitions(defs: Record<string, Definition>): void {
        Object.keys(defs).forEach((type: string): void => {
            const def = defs[type] // assigning value to a variable

            if (def) {
                this.addDefinition(type, def); // validating def
            }
        });
    }

The type undefined cannot be assigned to the type even with a null check

Answer №1

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