TypeScript-related error handling

TypeScript Error Handling

Error handling in TypeScript within Vite.js projects requires special attention to the type system and compile-time checking features. Vite's fast development experience combined with TypeScript's static type checking can significantly improve code quality, but it may also encounter some unique error scenarios.

Type Inference Error Handling

When Vite processes .ts files, it relies on TypeScript's type system. Common type errors include implicit any and type mismatches. For example:

// Error example: Implicit any type for parameters
function add(a, b) {
  return a + b
}

// Correct approach
function add(a: number, b: number): number {
  return a + b
}

When encountering type inference issues, you can resolve them in the following ways:

1. Explicitly declare type annotations
2. Use @ts-ignore to temporarily skip checks (not recommended for long-term use)
3. Configure the noImplicitAny option in tsconfig.json

Module Import Type Errors

Vite's module resolution approach may cause TypeScript errors, especially when dealing with third-party libraries:

// Common error: Missing module declaration
import someLib from 'untyped-lib'

// Solution 1: Add type declaration
declare module 'untyped-lib' {
  export default any
}

// Solution 2: Create types/untyped-lib.d.ts

For non-JS resources like CSS, add the following to vite-env.d.ts:

declare module '*.module.css' {
  const classes: { readonly [key: string]: string }
  export default classes
}

Common Errors in Strict Mode

Enabling strict: true will trigger more type checks. Typical issues include:

interface User {
  name: string
  age?: number
}

// Error: Possibly undefined
function getUserAge(user: User): number {
  return user.age  // Error: Object is possibly 'undefined'
}

// Solution 1: Type guard
if (user.age !== undefined) {
  return user.age
}

// Solution 2: Non-null assertion (ensure it is indeed not null)
return user.age!

Async Code Type Handling

When handling asynchronous operations in Vite projects, TypeScript requires explicit Promise types:

// Error: Implicit Promise<any>
async function fetchData() {
  const response = await fetch('/api/data')
  return response.json()
}

// Correct approach
interface ApiData {
  id: number
  value: string
}

async function fetchData(): Promise<ApiData> {
  const response = await fetch('/api/data')
  return response.json() as Promise<ApiData>
}

Generic Component Error Handling

When using Vue/React components, generic types often lead to complex errors:

// Vue component example
import { defineComponent } from 'vue'

interface Item {
  id: number
  name: string
}

// Error: Generic parameter not correctly passed
const GenericList = defineComponent({
  props: {
    items: Array // Missing generic parameter
  }
})

// Correct approach
const GenericList = defineComponent({
  props: {
    items: {
      type: Array as PropType<Item[]>,
      required: true
    }
  }
})

Environment Variable Type Handling

Vite's environment variables require special type handling:

1. Extend types in vite-env.d.ts:

interface ImportMetaEnv {
  readonly VITE_API_URL: string
  readonly VITE_DEBUG_MODE: boolean
}

2. Perform type validation when using them:

if (import.meta.env.VITE_DEBUG_MODE === 'true') {
  // Manual boolean conversion required
  const debugMode = import.meta.env.VITE_DEBUG_MODE === 'true'
}

Type Assertions and Guards

Inappropriate type assertions are a common source of errors:

// Dangerous type assertion
const element = document.getElementById('app') as HTMLElement

// Safer approach
const element = document.getElementById('app')
if (!element) throw new Error('Element not found')

// Custom type guard
function isUser(data: unknown): data is User {
  return typeof data === 'object' && data !== null && 'name' in data
}

Third-Party Library Type Extensions

When dealing with libraries without type definitions:

// Extend existing type declarations
declare module 'vue' {
  interface ComponentCustomProperties {
    $filters: {
      formatDate: (date: Date) => string
    }
  }
}

// Add properties to the window object
declare global {
  interface Window {
    myCustomGlobal: string
  }
}

Advanced Type Tool Usage

Issues when using TypeScript advanced types:

// Conditional type errors
type Status = 'success' | 'error'
type Result<T> = T extends 'success' ? string : Error

// Using infer
type UnwrapPromise<T> = T extends Promise<infer U> ? U : T

// Handling union types
function handleInput(input: string | number) {
  if (typeof input === 'string') {
    return input.toUpperCase()
  }
  return input.toFixed(2)
}

Vite-Specific Type Issues

TypeScript issues in Vite configuration:

// vite.config.ts
import { defineConfig } from 'vite'
import vue from '@vitejs/plugin-vue'

export default defineConfig({
  plugins: [vue()],
  server: {
    proxy: {
      // Requires correct typing
      '/api': {
        target: 'http://localhost:3000',
        changeOrigin: true,
        rewrite: (path) => path.replace(/^\/api/, '')
      }
    }
  }
})

Type Handling in Tests

Test code also requires type safety:

// Test example
import { mount } from '@vue/test-utils'
import Component from './Component.vue'

test('renders correctly', () => {
  const wrapper = mount(Component, {
    props: {
      // Must match component props type
      items: [{ id: 1, name: 'Test' }]
    }
  })
  
  expect(wrapper.text()).toContain('Test')
})

Build-Time Type Checking

Integrating type checking during Vite builds:

1. Install vite-plugin-checker:

npm install vite-plugin-checker --save-dev

2. Configure vite.config.ts:

import { defineConfig } from 'vite'
import checker from 'vite-plugin-checker'

export default defineConfig({
  plugins: [
    checker({
      typescript: true
    })
  ]
})

Type Compatibility Issues

Handling conflicts between browser APIs and Node.js types:

// Solving globalThis type issues
declare global {
  var __MY_GLOBAL__: string
}

// Handling DOM types
const canvas = document.createElement('canvas')
const ctx = canvas.getContext('2d')
if (!ctx) throw new Error('Context not supported')

// Handling differences between Node.js and browser environments
type ProcessEnv = typeof process.env

Type Export and Import

Common issues with module system type exports:

// Correct type export
export interface User {
  id: number
  name: string
}

// Separating types and values during import
import type { User } from './types'
import { fetchUser } from './api'

// Re-exporting types
export type { User } from './types'

Type and Runtime Validation

Combining with libraries like zod for runtime type validation:

import { z } from 'zod'

const UserSchema = z.object({
  id: z.number(),
  name: z.string()
})

type User = z.infer<typeof UserSchema>

function validateUser(data: unknown): User {
  return UserSchema.parse(data)
}