how should i handle this peer dependancy error on npm in my angular 10 project?

Question

I am upgrding my angular 10 project which running in node 14.x and npm 6.14.x and while i do

npm ls

the following problems are displayed in npm,

"problems": [
    "peer dep missing: @angular/common@^9.0.0, required by @fullcalendar/[email protected]",
    "peer dep missing: @angular/common@^9.0.0, required by @ng-idle/[email protected]",
    "peer dep missing: @angular/common@^9.0.0, required by @ng-idle/[email protected]",
    "peer dep missing: @angular/common@^9.0.0, required by @ngx-toolkit/[email protected]",
    "peer dep missing: @angular/common@^6.0.0 || ^7.0.0 || ^8.0.0 || ^9.0.0, required by [email protected]",
    "peer dep missing: @angular/core@^9.0.0, required by @fullcalendar/[email protected]",
    "peer dep missing: @angular/core@^9.0.0, required by @ng-idle/[email protected]",
    "peer dep missing: @angular/core@^9.0.0, required by @ng-idle/[email protected]",
    "peer dep missing: @angular/core@^9.0.0, required by @ngx-toolkit/[email protected]",
    "peer dep missing: @angular/core@ ^6.0.0 || ^7.0.0 || ^8.0.0 || ^9.0.0, required by [email protected]",
    "peer dep missing: jest@^24.1.0, required by [email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: [email protected] - 3, required by [email protected]",
    "peer dep missing: popper.js@^1.16.0, required by [email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: jest@^24.1.0, required by [email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: jest@>=24 <25, required by [email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @fullcalendar/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]",
    "peer dep missing: tslib@^1.10.0, required by @ng-idle/[email protected]"
  ]

so what should i do to fix these problems ? (please keep in mind i am trying to upgrade node and npm here),seems like peer dependancy errors and should i go with npm install --legacy-peer-deps ?

A solution to fix all these peer dependency errors ?

Answer 1

When upgrading your project to a newer version of Angular it's best to follow the angular update guide and use ng upgrade to update. Many first-party Angular packages are dependant on each other and only work together when using the versions defined by the Angular team.

Any third-party Angular libraries (when built properly) define peerDependencies in their package.json to tell you with which versions their package has been tested and will probably work. Any newer major versions are not guaranteed to work.

When looking at the output of npm ls I think you either:

• forgot to update third-party Angular packages, or
• the third-party packages you are using are not yet officially supporting the Angular version you updated to, or
• both

So I advise you to first try to update your third-party packages (preferably using ng update) and if the warnings persist just give your app a try. If it does not work, then you have to wait for support...