The pseudo class ":first-child" is potentially unsafe when doing server-side rendering. Try changing it to ":first-of-type"

Question

I got this error, although there is not a single line in the project with :first-child, why does it appear?

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 "dependencies": {
    "@storybook/addon-a11y": "^5.1.9",
    "@trendmicro/react-popover": "^0.4.0",
    "@types/classnames": "^2.2.9",
    "@types/jest": "24.0.13",
    "@types/node": "12.0.2",
    "@types/react": "16.8.18",
    "@types/react-dom": "16.8.4",
    "@types/react-modal": "^3.8.2",
    "@types/storybook__addon-a11y": "^5.0.0",
    "@types/storybook__addon-actions": "^3.4.3",
    "@types/storybook__addon-info": "^4.1.1",
    "@types/storybook__addon-knobs": "^5.0.0",
    "@types/storybook__react": "4.0.1",
    "@types/styled-components": "4.1.15",
    "classnames": "^2.2.6",
    "grommet": "^2.7.2",
    "react": "16.8.6",
    "react-dom": "16.8.6",
    "react-modal": "^3.9.1",
    "react-scripts": "3.0.1",
    "react-toastify": "^5.3.2",
    "styled-components": "^4.2.0",
    "typescript": "^3.5.1"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject",
    "storybook": "start-storybook",
    "build-storybook": "build-storybook -c .storybook -o .out",
    "lint": "tslint -c tslint.json src/**/*.{ts,tsx} --fix --format verbose",
    "tslint-check": "tslint-config-prettier-check ./tslint.json",
    "precommit": "lint-staged"
  },
  "lint-staged": {
    "{src,test}/**/*.{ts,tsx}": [
      "prettier --write",
      "git add"
    ]
  },
  "eslintConfig": {
    "extends": "react-app"
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  },
  "devDependencies": {
    "@storybook/addon-actions": "5.1.9",
    "@storybook/addon-info": "^5.1.9",
    "@storybook/addon-knobs": "^5.1.9",
    "@storybook/addon-links": "5.1.9",
    "@storybook/addon-storysource": "^5.1.9",
    "@storybook/addons": "5.1.9",
    "@storybook/core-events": "latest",
    "@storybook/react": "5.1.9",
    "@storybook/theming": "latest",
    "husky": "^3.0.0",
    "lint-staged": "^9.1.0",
    "react-docgen-typescript-loader": "3.1.0",
    "react-docgen-typescript-webpack-plugin": "1.1.0",
    "storybook-addon-styled-component-theme": "^1.2.3",
    "ts-loader": "^6.0.4",
    "tslint": "^5.18.0",
    "tslint-config-airbnb": "^5.11.1",
    "tslint-config-prettier": "^1.18.0",
    "tslint-plugin-prettier": "^2.0.1",
    "tslint-react": "^4.0.0"
  }

Eileen

it could be from one of the dependencies, try searching inside node_modules – Degrading

but if I need this module I can’t get rid of this error? – Appetence

I'm pretty sure this will only be logged in development mode. You can ignore it probably – Keratinize

I need to remove all errors from the console, I just can not ignore =( – Appetence

Probably related to github.com/storybookjs/storybook/issues/6998 – Smectic

I am not able rightly to apprehend the kind of confusion of ideas that could provoke such an error message. – Southernmost

I am seeing the same exact issue in Angular version of StoryBook. – Tideway

The warning comes from @emotion which is a dependency of Storybook. If you are not doing SSR you can safely ignore it, but I agree it is annoying. – Uncover

Answer 1

This comes from @emotion through storybook - since emotion (creates CSS through JavaScript) sometimes injects a <style> element in the beginning - which would make that the first child and breaks your CSS. first-of-type is supported in most browsers these days and can be used in many cases alternatively.

Now since you said you don't actually have a line with a first-child pseudo selector it is most likely storybook themselves using an "unsafe" CSS rule.

Lop

Answer 2

This seems to have been a well-known issue for a while with storybook.

Try upgrading to >= 6.5.8 – the issue should be fixed from that version onwards.

Dena

I'm on storybook 6.5.9 and having this error. Seems like they have re-introduced it then: github.com/storybookjs/storybook/issues/18656 – Leopard