the syntax requires an imported helper named __spreadArrays

Question

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.

Answer 1

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 .

Answer 2

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

Answer 3

This error might happen if you have in your tsconfig.json file:

{ 
  "importHelpers": true,
  "target": "es5"
}

If for any reason you can't upgrade to es6, setting importHelpers to false will make the error go away...

Answer 4

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.

Answer 5

Assuming your tslib is installed correctly and up to date, you might still get this error in VS Code if the editor is using a different Typescript version.

(taken from zok's answer on this SO question )

Open Command Palette (Cmd+Shift+P on Mac. Focused file must be.ts or.tsx otherwise it won't show the option to change version) Select "TypeScript: Select TypeScript Version..." It shows VSCode's TS version and Workspace's (project) one, pick the workspace one

Answer 6

for yarn users: yarn upgrade tslib@latest

Answer 7

from right side down hover on curly braces beside of TypeScript and then click on version it will give you few options, generally related to project just select version and it will work fine

Answer 8

you may need to upgrade to tslib@2.2.0

Answer 9

Just make sure tslint is enabled in the bottom of vscode editor options

Answer 10

Ran into this issue with a dependency and resolved it by updating its tsconfig.ts with the path to the top level lastest tslib .

"importHelpers": true,
"paths": {
  "tslib": [ "../tslib/tslib.d.ts" ]
}