Encountering a tuple type TypeScript error with a spread argument is far too frequent an occurrence

Question

Encountering a tuple type TypeScript error with a spread argument is far too frequent an occurrence

Encountering this error is becoming a frequent occurrence for me, and I am currently unable to resolve it.

src/graphics.ts:105:55 - error TS2556: A spread argument must either have a
tuple type or be passed to a rest parameter.

105       _queue.forEach((_: any[]) => draw_ctx(this.ctx, ..._))
                                                          ~~~~

Below is the snippet of code where the error arises:

export default class Graphics {

  _queues: any

  constructor(readonly ctx: number) {
    this._queues = {}
  }

  flush() {
      Object.keys(this._queues).map(color => {
      let _queue = this._queues[color]
      _queue.forEach((_: any[]) => draw_ctx(this.ctx, ..._))
    })
  }
}


function draw_ctx(ctx: number, _f: any, r: number, x: number, y: number, w: number, h: number, ...rest: any) {
    console.log('hello')
}

Additionally, provided below is the content of tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2020",
    "useDefineForClassFields": true,
    "module": "ESNext",
    "lib": ["ESNext", "DOM", "DOM.Iterable"],
    "skipLibCheck": true,

    /* Bundler mode */
    "moduleResolution": "bundler",
    "allowImportingTsExtensions": true,
    "resolveJsonModule": true,
    "isolatedModules": true,
    "noEmit": true,

    /* Linting */
    "strict": true,
    //"noUnusedLocals": true,
    //"noUnusedParameters": true,
    "noFallthroughCasesInSwitch": true
  },
  "include": ["src"]
}

typescript

Answer 1

Answer №1

Arrays and tuples are not the same thing. Tuples have a fixed number of elements, while arrays do not.

TypeScript needs to ensure that the array you pass as an argument meets the requirements of the draw_ctx function.

To satisfy TypeScript, make sure the signature of the _ argument matches the arguments expected by draw_ctx:

_queue.forEach((_:[any, number, number, number, number, number, ...any]) => draw_ctx(this.ctx, ..._))

By defining an array with a fixed number of elements, you can meet TypeScript's expectations.

Note that there are still improvements needed in this code. Instead of casting types, it's better to define proper types like this._queues so that TypeScript enforces correct typing:

export default class Graphics {

  _queues:{[color:string]:[any, number, number, number, number, number, ...any][]}

  constructor(readonly ctx: number) {
    this._queues = {}
  }

  flush() {
      Object.keys(this._queues).map(color => {
      let _queue = this._queues[color]
      _queue.forEach((_) => draw_ctx(this.ctx, ..._))
    })
  }
}

function draw_ctx(ctx: number, _f: any, r: number, x: number, y: number, w: number, h: number, ...rest: any) {
    console.log('hello')
}

link

It may seem like adding

this._queues["crash"] = "this will crash the program in runtime"

works in your code, but results in an error in mine.

Remember: Avoid using any in TypeScript to maintain strong typing. Using any can introduce JavaScript-like issues, undermining the purpose of TypeScript.

Answer 2

Arrays and tuples are not the same thing. Tuples have a fixed number of elements, while arrays do not.

TypeScript needs to ensure that the array you pass as an argument meets the requirements of the draw_ctx function.

To satisfy TypeScript, make sure the signature of the _ argument matches the arguments expected by draw_ctx:

_queue.forEach((_:[any, number, number, number, number, number, ...any]) => draw_ctx(this.ctx, ..._))

By defining an array with a fixed number of elements, you can meet TypeScript's expectations.

Note that there are still improvements needed in this code. Instead of casting types, it's better to define proper types like this._queues so that TypeScript enforces correct typing:

export default class Graphics {

  _queues:{[color:string]:[any, number, number, number, number, number, ...any][]}

  constructor(readonly ctx: number) {
    this._queues = {}
  }

  flush() {
      Object.keys(this._queues).map(color => {
      let _queue = this._queues[color]
      _queue.forEach((_) => draw_ctx(this.ctx, ..._))
    })
  }
}

function draw_ctx(ctx: number, _f: any, r: number, x: number, y: number, w: number, h: number, ...rest: any) {
    console.log('hello')
}

link

It may seem like adding

this._queues["crash"] = "this will crash the program in runtime"

works in your code, but results in an error in mine.

Remember: Avoid using any in TypeScript to maintain strong typing. Using any can introduce JavaScript-like issues, undermining the purpose of TypeScript.

Answer 3

Answer №2

The reason for this issue is that the type of _ is any[], causing TypeScript to be unable to match the correct number of parameters for draw_ctx. One way around this is demonstrated below:

draw_ctx(this.ctx, 'foo', 1, 2, 3, 4, 5, ..._)

If needed, you can disable this rule for a specific line by using the following syntax:

// @ts-ignore: A spread argument must either have a tuple type or be passed to a rest parameter.
draw_ctx(this.ctx, ..._)

Answer 4

The reason for this issue is that the type of _ is any[], causing TypeScript to be unable to match the correct number of parameters for draw_ctx. One way around this is demonstrated below:

draw_ctx(this.ctx, 'foo', 1, 2, 3, 4, 5, ..._)

If needed, you can disable this rule for a specific line by using the following syntax:

// @ts-ignore: A spread argument must either have a tuple type or be passed to a rest parameter.
draw_ctx(this.ctx, ..._)

Encountering a tuple type TypeScript error with a spread argument is far too frequent an occurrence

Answer №1

Answer №2

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