the syntax requires an imported helper named __spreadArrays

When I'm trying to use spreading in typescript like:

.reduce((unique, x) => {
    unique.some(element => element.machineName === x.machineName) ? unique : [...unique, x];
}

I get warning with red marking from Visual Studio Code:

the syntax requires an imported helper named __spreadArrays

typescript version: "2.3.4"
target: "es5"

I think in later versions this issue is fixed, but right now I can't migrate. How can I fix it?

Note: Project gets compiled fine and works. But red underlying in VS Code in annoying.

In my case the problem it was target: "es5" in compilerOptions at tsconfig.json.

So I change it to es6 to get it works without adding dependency.

Quick fix, short answer

npm install tslib@latest --save

I got this issue again (now with tslib version 2.2.0) after updating VS Code, again updating fixed the issue.

I had this issue with tslib version 1.14.1

npm update tslib --save didn't really do anything

npm install tslib@latest --save did the job, it updated to version 2.2.0

For VS Code the notification is based on the tsLib exports. Actually nothing bad happens without doing anything, it is just lack of typing.

Solution: Update tsLib dependency to get rid of the highlighting. In my case it was version 1.9.0. Update to 1.10.0 solved the issue.

__spreadArrays is added in 1.10.0 tsLib version: https://github.com/microsoft/tslib/blob/1.10.0/tslib.es6.js

Update: Since some time passed, it is better to update version to 2.2.0 (based on last comments) or the latest.