# @typescript-eslint/no-unnecessary-type-conversion

> Disallow converting a value to the type it already has

`String(name)`, `+count` and `!!isOpen` all convert a value. If `name` is already a string, `count` is already a number and `isOpen` is already a boolean, they convert nothing, and the reader is left wondering what else the value could have been.

| Reported | If the value is already |
| --- | --- |
| `String(x)`, `x.toString()`, `x + ""`, `"" + x`, `x += ""` | a string |
| `Number(x)`, `+x` | a number |
| `Boolean(x)`, `!!x` | a boolean |
| `BigInt(x)` | a bigint |
| `~~x` | an integer literal type, such as `3` |

{/* Generated by src/codegen/lint-rule-docs.ts. Do not edit this section. */}

## Configure

Off by default. This rule needs types, so turning it on makes `bun lint` type check your code first.

```toml bunfig.toml
[lint.rules]
"@typescript-eslint/no-unnecessary-type-conversion" = "error" # or "warn"
```

{/* End of the generated section. */}

## Examples

Reported:

{/* bad {"count": 4} */}
```ts
function format(name: string, count: number, isOpen: boolean) {
  const label = String(name);
  const title = name.toString() + ":";
  const total = +count;
  const open = !!isOpen;
  return [label, title, total, open];
}
```

Not reported:

{/* good */}
```ts
function format(name: string, count: number, isOpen: boolean) {
  const label = name;
  const total = count;
  const open = isOpen;
  return [label, total, open];
}
```

A conversion that changes the type isn't reported:

{/* good */}
```ts
function read(input: string, id: number | string, user?: object) {
  const count = Number(input);
  const key = String(id);
  const isKnown = !!user;
  return [count, key, isKnown];
}
```