Using bracket notation to access object prop with type 'undefined' is not allowed in TypeScript

Within my for loop, I am retrieving the name and id of each credential in the following manner:

    for (const cred of provider.credentials || []) {
        const credId = cred.id
        const credName = cred.name
        const credValue = state[credName]
    }

Yet, I encounter an error referenced in the title while establishing credValue.

I suspect the issue arises when credName is potentially null. Even though I attempt to utilize the Non-null assertion operator as a solution, my attempts have not yielded success.

To clarify, the structure of the state object consistently resembles this:

state: {
   cred1: 'value'
   cred2: 'value'
}

Answer №1

To inform the ts compiler that credName is a key within state, follow these steps:

Give this approach a try:

let state = {
   cred1: 'value1',
   cred2: 'value2'
}

type StateKeyType = keyof typeof state;

for (const cred of provider.credentials || []) {
    const credId = cred.id
    const credName = cred.name as StateKeyType
    const credValue = state[credName]
}

Take a look at the PlaygroundLink for reference

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