Object is possibly 'undefined'

TypeScript Version: 3.4.0-dev.201xxxxx

Search Terms: Object undefined

Code turn strictNullChecks on

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.
type EventType = 'click' | 'dblclick'

const handlerMap: { [P in EventType]?: any[] } = {}

function addHandler<P extends EventType>(evType: P) {
  const handlerList = handlerMap[evType] || []
  handlerList.push({}) // Error here: Object is possibly 'undefined'
  handlerMap[evType] = handlerList
}

Expected behavior: No Error

Actual behavior: Shows Error

Playground Link: http://www.typescriptlang.org/play/#src=type%20EventType%20%3D%20'click'%20%7C%20'dblclick'%0Aconst%20handlerMap%3A%20%7B%20%5BP%20in%20EventType%5D%3F%3A%20any%5B%5D%20%7D%20%3D%20%7B%7D%0Afunction%20addHandler%3CP%20extends%20EventType%3E(evType%3A%20P)%20%7B%0A%20%20const%20handlerList%20%3D%20handlerMap%5BevType%5D%20%7C%7C%20%5B%5D%0A%20%20handlerList.push(%7B%7D)%20%2F%2F%20Error%20here%3A%20Object%20is%20possibly%20'undefined'%0A%7D%0A

Related Issues:

Will be giving this a try.

It's the same issue?

interface State {
    [i: string]: {data?: {id:string}} | undefined
 }

declare var x: State;

const id = 'xx';
const y = x[id] && x[id].data; // Error: Object is possibly 'undefined' (with strictNullChecks
const yId = y && y.id; // correct type – string | undefined

Playground link : https://www.typescriptlang.org/play/#src=interface%20State%20%7B%0D%0A%20%20%20%20%5Bi%3A%20string%5D%3A%20%7Bdata%3F%3A%20%7Bid%3Astring%7D%7D%20%7C%20undefined%0D%0A%20%7D%0D%0A%0D%0Adeclare%20var%20x%3A%20State%3B%0D%0A%0D%0Aconst%20id%20%3D%20'xx'%3B%0D%0A%0D%0Aconst%20y%20%3D%20x%5Bid%5D%20%26%26%20x%5Bid%5D.data%3B%0D%0A%0D%0Aconst%20yId%20%3D%20y%20%26%26%20y.id%3B%0D%0A

Collins Abitekaniza (@collin5)

#29317 should be the fix here (which I have mentioned in Collins Abitekaniza (@collin5) 's PR). Specifically, the type of a || b should be calculated as (typeof a & not FalseyTypes) | typeof b, where FalseyTypes is 0 | false | "" | undefined | null.

Ryan Cavanaugh (@RyanCavanaugh) given that, should we move this out of 3.4, since we won't be shipping them in 3.4?

Stanislav Svirid (@ktoto)

Stanislav Svirid (@ktoto) your issue is different - since State has an index signature, we don't track refinements on individual property lookups within it - see #17960 and #29042 (and go updoot those issues so they don't sit in the backlog).

I have same issue. :(

Typescript Version : 3.4.5

Mufid Jamaluddin (@MufidJamaluddin)

Mufid Jamaluddin (@MufidJamaluddin) duplicate of #7719

Workaround is use kelas!.iskelas

Mufid Jamaluddin (@MufidJamaluddin)

Same issue as Mufid Jamaluddin (@MufidJamaluddin)
I have a checker in place to avoid duplicating code but Typescript ignores it and output this error.

Tracking at #7719

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

Ryan Cavanaugh (@RyanCavanaugh)

Ryan Cavanaugh (@RyanCavanaugh) did you link the wrong issue? That one has been closed since 2018.

Also having this issue

Code

type Key = "key1" | "key2";
type Keys = {
  [P in Key]?: { keyProp: string };
};

const keys: Keys = {
  key1: { keyProp: "keyPropVal" },
};

let someKey!: Key;

if (keys[someKey]) {
  // This shows Object is possibly 'undefined'
  keys[someKey].keyProp;
}

Output

"use strict";
const keys = {
    key1: { keyProp: "keyPropVal" },
};
let someKey;
if (keys[someKey]) {
    // This shows Object is possibly 'undefined'
    keys[someKey].keyProp;
}

Compiler Options

{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": false,
    "alwaysStrict": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "downlevelIteration": false,
    "noEmitHelpers": false,
    "noLib": false,
    "noStrictGenericChecks": false,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "esModuleInterop": true,
    "preserveConstEnums": false,
    "removeComments": false,
    "skipLibCheck": false,
    "checkJs": false,
    "allowJs": false,
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false,
    "target": "ES2017",
    "module": "ESNext"
  }
}

Playground Link: Provided

Hello All,

The object is possibly 'undefined',

This warning is shown by the editor when we provide the body definition of some variable in the form of the interface and add some of the fields as optional

Eg:-

interface Blog {
  autherName: string;
  contents?: any[],
  id: string
}

While using this interface Blog in our code if we are trying to do some loop on Blog.contents
Eg:-

const newBlog: Blog = JSON.parse(blog);
for (const content of newBlog.contents) {`
   console.log("content ", content );
}

This will error in for loop declaration for (const content of newBlog.contents) because we have said in an interface that contents property in Blob object can be or cannot be there hence we first need to check in code if the property is present then we should use it. As follows

Eg:-

if (newBlog.contents && newBlog.contents.length > 0) {
    for (const content of newBlog.contents) {
      console.log("content ", content );
   }
}

This is one way to resolve this warning.

Happy Coding!

Hello All,

The object is possibly 'undefined',

This warning is shown by the editor when we provide the body definition of some variable in the form of the interface and add some of the fields as optional

Eg:-
interface Blog {
  autherName: string;
  contents?: any[],
  id: string
}
While using this interface Blog in our code if we are trying to do some loop on Blog.contents
Eg:-
const newBlog: Blog = JSON.parse(blog);
for (const content of newBlog.contents) {`
   console.log("content ", content );
}
This will error in for loop declaration for (const content of newBlog.contents) because we have said in an interface that contents property in Blob object can be or cannot be there hence we first need to check in code if the property is present then we should use it. As follows

Eg:-
if (newBlog.contents && newBlog.contents.length > 0) {
    for (const content of newBlog.contents) {
      console.log("content ", content );
   }
}
This is one way to resolve this warning.

Happy Coding!

Thanks alokadhao20,It solved issue for me.

Ryan Cavanaugh (@RyanCavanaugh)

Ryan Cavanaugh (@RyanCavanaugh) did you link the wrong issue ? That one has been closed since 2018.

Locking because everyone is posting about all of their "is possibly undefined" code snippets here without context for the original post.

The inability to handle x || [] when x is a type parameter is a current design limitation wherein we need to have some new mechanism for describing higher-order facts about generic type parameters; today if something is T and we know it's truthy or falsy, there's no mechanism for us to better describe its assignability to any given target type. Everything we've tried so far here has been a performance or usability disaster so it's on the back burner for the time being until we can hopefully have some better insight on how to represent this in a more ergonomic/efficient way.

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Object is possibly 'undefined' #29642

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Object is possibly 'undefined' #29642

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collin5 commented on Feb 1, 2019

ktoto commented on Feb 18, 2019

weswigham commented on Mar 14, 2019

weswigham commented on Mar 14, 2019

MufidJamaluddin commented on May 10, 2019

troy351 commented on May 10, 2019

micky2be commented on Jun 13, 2019

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