The TypeScript feature Array.find may potentially return undefined, yet it is always treated as a specific data type

There's a minor obstacle blocking my way:

const foo = ["foo", "bar"]; // type "string[]"
const foundFoo = foo.find(fooEl => fooEl === "notFooBar"); // type "string" -> why not "string | undefined"

After reviewing the type definitions of array.find, I noticed that it does mention the possibility of returning undefined. However, my environment is indicating that foundFoo is of type string instead of string | undefined. Why is this discrepancy occurring?

Upon searching StackOverflow for similar queries, most questions were about why it "could" be undefined, so I'm unsure why my environment is displaying the opposite result.

Answer №1

Ensure that you have the strictNullChecks setting enabled in your tsconfig.json configuration file. Without this option activated, all types (excluding any) will essentially default to T | undefined:

When operating under strict null checking mode, the values null and undefined are not included in the domain of every type and can only be assigned to themselves and any (with the exception of void accepting undefined as well).

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