typescript - Compilation error on casting query selector result to HTMLElement inside a vue component's <script lang="ts"> code

Question

One of components in my Vuejs based project has the following mounted method

mounted() {
  try {
    let x = 'abc';
    console.log(x);
    let body = <HTMLElement> document.querySelector("body");
  } catch (e) {
    console.log(e);
  }
}

where the compilation (i-e vue-cli-service lint file_path) is failing with error

Parsing error: Unexpected token, expected "}"
console.log(e);
......................^

My eslintrc.js looks like this (with babel-eslint as the parser)

module.exports = {
  root: true,
  env: {
    node: true,
  },
  extends: [
    'plugin:vue/essential',
  ],
  rules: {
    quotes: ['error', 'single']
  },
  parserOptions: {
    parser: 'babel-eslint',
  }
};

package.json has following dependencies

"dependencies": {
    "@amcharts/amcharts4": "^4.6.1",
    "@sentry/browser": "^5.17.0",
    "@sentry/integrations": "^5.17.0",
    "@types/node": "^10.12.9",
    "@vue/cli-plugin-eslint": "^3.0.0-rc.3",
    "@vue/cli-plugin-typescript": "^3.0.0-rc.3",
    "@vue/cli-plugin-unit-mocha": "^3.0.0-rc.3",
    "@vue/cli-service": "3.9.3",
    "axios": "^0.15.3",
    "element-ui": "^2.8.2",
    "har-validator": "^5.1.3",
    "less-loader": "^4.1.0",
    "lodash": "^4.17.2",
    "moment": "^2.20.1",
    "typescript": "^3.0.1",
    "vee-validate": "^2.1.0-beta.7",
    "vue": "^2.5.16",
    "vue-authenticate": "^1.4.1",
    "vue-class-component": "^6.0.0",
    "vue-debounce": "^2.0.0",
    "vue-froala-wysiwyg": "^2.9.1",
    "vue-property-decorator": "^6.0.0",
    "vue-router": "^3.0.1",
    "vue-typeahead": "^2.3.0",
    "vuedraggable": "^2.21.0",
    "vuescroll": "^4.16.1",
    "vuetify": "1.1.0",
    "vuex": "^3.0.1",
    "vuex-router-sync": "^3.0.0",
    "vuex-saga": "^0.1.3"
  },
  "devDependencies": {
    "@types/chai": "^4.1.0",
    "@types/jest": "^23.3.10",
    "@types/mocha": "^2.2.46",
    "@types/webpack-env": "^1.15.2",
    "@vue/eslint-config-typescript": "^3.0.0-rc.3",
    "@vue/test-utils": "^1.1.0",
    "babel-core": "^6.26.0",
    "babel-jest": "^22.1.0",
    "babel-loader": "^7.1.2",
    "babel-polyfill": "^6.26.0",
    "babel-preset-env": "^1.6.1",
    "babel-preset-es2015": "^6.24.1",
    "babel-preset-stage-2": "^6.24.1",
    "babel-preset-stage-3": "^6.24.1",
    "chai": "^4.1.2",
    "dotenv": "^6.0.0",
    "faker": "^4.1.0",
    "file-system": "^2.2.2",
    "flush-promises": "^1.0.2",
    "jasmine-core": "^3.3.0",
    "jest": "^22.1.4",
    "jest-vue": "^0.8.2",
    "jquery": "^3.5.1",
    "less": "~3.9.0",
    "lint-staged": "^6.0.0",
    "regenerator-runtime": "^0.11.1",
    "ts-jest": "^23.0.1",
    "vue-jest": "^3.0.2",
    "vue-router": "^3.0.1",
    "vue-template-compiler": "^2.5.16"
  }

What could be causing this issue ? Btw, running eslint file_path gives the same error.

question from:https://stackoverflow.com/questions/65837599/compilation-error-on-casting-query-selector-result-to-htmlelement-inside-a-vue-c

Answer 1

According to Typescript Documentation,

...when using TypeScript with JSX, only as-style assertions are allowed.

(Meaning angle-bracket-style assertions are not allowed).

Even though JSX usage in Vue is rare, Vue is JSX compatible. Meaning you have to limit your type assertions to as-style. In other words, replace

let body = <HTMLElement> document.querySelector("body");

with either

const body = document.querySelector("body") as HTMLElement;

or

const body: HTMLElement = document.querySelector("body");

Note: replacing let with const is irrelevant for the question being asked, but if you never reassign to body, you should use const.