CODEWITHSUNDEEP
typescript
financial_physician
financial_physician

Reputation: 1998

Typescript thinks object may be undefined even though it is defined

I found a post with a similar name although the problem is different.

I'm trying to count the number of occurrences of an attribute in a list of a objects.

let objArray = [{state: 'North Carolina'},{state: 'Florida'}]

let res = new Map<string, number>();
for (let obj of objArray) {
    if (res.get(obj.state)) {
      res.set(obj.state, res.get(obj.state)+1)
    } else {
      res.set(obj.state, 1)
    }
}

But typescript flags res.get(obj.state) + 1 because res.get(obj.state) may be undefined (which I don't think is possible).

I'd also be equally fine with let res = {} but when I write analogous code for that typescript doesn't like trying to index res by string.

I'm kinda at a loss for what typescript expects me to do to accomplish my simple task.

Upvotes: 1

Views: 457

Answers (2)

Harald Gliebe
Harald Gliebe

Reputation: 7564

The TypeScript compiler should be happy if you extract the repeated use of res.get(obj.state) into a variable:

let objArray = [{state: 'North Carolina'},{state: 'Florida'}]

let res = new Map<string, number>();
for (let obj of objArray) {
    const state = res.get(obj.state);
    if (state) {
      res.set(obj.state, state+1)
    } else {
      res.set(obj.state, 1)
    }
}

Upvotes: 5

user16442705
user16442705

Reputation:

Adding ! seems to work:

res.get(obj.state)! + 1

Playground link

Upvotes: 0

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