'Object is possibly undefined' for items in an array

Question

I know there are a lot of questions about 'Object is possibly undefined' errors in typescript, but I have not found an answer to my particular question. I have an array with items and I want to access an element by index. I can put checks for each part of the element I want to access in an if statement around it, but it will still tell me that it is possibly undefined.

My code looks like this:

if(this.classLevels && this.classLevels[finalLevel] && this.classLevels[finalLevel].class){
    this.classLevels[finalLevel].class.currentLevel += 1;
}

class seems to be what can be undefined. It automatically wants to put a questionmark there, like this.classLevels[finalLevel].class?.currentLevel += 1;, but in that case I get the error that The left-hand side of an assignment expression may not be an optional property access.

I don't really want to disable the strict undefined check, but if I cannot get it to work with elements in an array, I may have to. Is there something I am missing here?

spender · Accepted Answer · 2021-08-11 10:39:02Z

3

Assuming that you have noUncheckedIndexedAccess enabled, your best bet would be to make an intermediate variable:

const finalLevelClass = this.classLevels?.[finalLevel]?.class;

if (finalLevelClass) {
    finalLevelClass.currentLevel += 1;
}

answered Aug 11, 2021 at 10:39

spender

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1 Comment

Erian Over a year ago

This works, thank you. I didn't know this was comming from a different typescript flag than the other error.

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