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docs(eslint-plugin): [prefer-nullish-coalescing] streamline code examples#10735

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150 changes: 91 additions & 59 deletionspackages/eslint-plugin/docs/rules/prefer-nullish-coalescing.mdx
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Original file line numberDiff line numberDiff line change
Expand Up@@ -28,46 +28,48 @@ This rule will not work as expected if [`strictNullChecks`](https://www.typescri

{/* insert option description */}

Incorrect code for `ignoreTernaryTests: false`, and correct code for `ignoreTernaryTests: true`:

```ts option='{ "ignoreTernaryTests": false }' showPlaygroundButton
const foo: any = 'bar';
foo !== undefined && foo !== null ? foo : 'a string';
foo === undefined || foo === null ? 'a string' : foo;
foo == undefined ? 'a string' : foo;
foo == null ? 'a string' : foo;

const foo: string | undefined = 'bar';
foo !== undefined ? foo : 'a string';
foo === undefined ? 'a string' : foo;

const foo: string | null = 'bar';
foo !== null ? foo : 'a string';
foo ? foo : 'a string';
foo === null ? 'a string' : foo;
!foo ? 'a string' : foo;
Examples of code for this rule with `{ ignoreTernaryTests: false }`:

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "ignoreTernaryTests": false }'
declare const a: any;
a !== undefined && a !== null ? a : 'a string';
a === undefined || a === null ? 'a string' : a;
a == undefined ? 'a string' : a;
a == null ? 'a string' : a;

declare const b: string | undefined;
b !== undefined ? b : 'a string';
b === undefined ? 'a string' : b;
b ? b : 'a string';
!b ? 'a string' : b;

declare const c: string | null;
c !== null ? c : 'a string';
c === null ? 'a string' : c;
c ? c : 'a string';
!c ? 'a string' : c;
```

Correct code for `ignoreTernaryTests: false`:
</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "ignoreTernaryTests": false }' showPlaygroundButton
const foo: any = 'bar';
foo ?? 'a string';
foo ?? 'a string';
foo ?? 'a string';
foo ?? 'a string';
```ts option='{ "ignoreTernaryTests": false }'
declare const a: any;
a ?? 'a string';

const foo: string | undefined = 'bar';
foo ?? 'a string';
foo ?? 'a string';
declare const b: string | undefined;
b ?? 'a string';

const foo: string | null = 'bar';
foo ?? 'a string';
foo ?? 'a string';
foo ?? 'a string';
foo ?? 'a string';
declare const c: string | null;
c ?? 'a string';
```

</TabItem>
</Tabs>

### `ignoreConditionalTests`

{/* insert option description */}
Expand All@@ -76,9 +78,12 @@ Generally expressions within conditional tests intentionally use the falsy fallt

If you're looking to enforce stricter conditional tests, you should consider using the `strict-boolean-expressions` rule.

Incorrect code for `ignoreConditionalTests: false`, and correct code for `ignoreConditionalTests: true`:
Examples of code for this rule with `{ ignoreConditionalTests: false }`:

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "ignoreConditionalTests": false }' showPlaygroundButton
```ts option='{ "ignoreConditionalTests": false }'
declare const a: string | null;
declare const b: string | null;

Expand All@@ -93,9 +98,10 @@ for (let i = 0; a || b; i += 1) {}
a || b ? true : false;
```

Correct code for `ignoreConditionalTests: false`:
</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "ignoreConditionalTests": false }' showPlaygroundButton
```ts option='{ "ignoreConditionalTests": false }'
declare const a: string | null;
declare const b: string | null;

Expand All@@ -110,6 +116,9 @@ for (let i = 0; a ?? b; i += 1) {}
(a ?? b) ? true : false;
```

</TabItem>
</Tabs>

### `ignoreMixedLogicalExpressions`

{/* insert option description */}
Expand All@@ -118,9 +127,12 @@ Generally expressions within mixed logical expressions intentionally use the fal

If you're looking to enforce stricter conditional tests, you should consider using the `strict-boolean-expressions` rule.

Incorrect code for `ignoreMixedLogicalExpressions: false`, and correct code for `ignoreMixedLogicalExpressions: true`:
Examples of code for this rule with `{ ignoreMixedLogicalExpressions: false }`:

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "ignoreMixedLogicalExpressions": false }' showPlaygroundButton
```ts option='{ "ignoreMixedLogicalExpressions": false }'
declare const a: string | null;
declare const b: string | null;
declare const c: string | null;
Expand All@@ -133,9 +145,10 @@ a || (b && c) || d;
a || (b && c && d);
```

Correct code for `ignoreMixedLogicalExpressions: false`:
</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "ignoreMixedLogicalExpressions": false }' showPlaygroundButton
```ts option='{ "ignoreMixedLogicalExpressions": false }'
declare const a: string | null;
declare const b: string | null;
declare const c: string | null;
Expand All@@ -148,6 +161,9 @@ a ?? (b && c) ?? d;
a ?? (b && c && d);
```

</TabItem>
</Tabs>

**_NOTE:_** Errors for this specific case will be presented as suggestions (see below), instead of fixes. This is because it is not always safe to automatically convert `||` to `??` within a mixed logical expression, as we cannot tell the intended precedence of the operator. Note that by design, `??` requires parentheses when used with `&&` or `||` in the same expression.

### `ignorePrimitives`
Expand All@@ -156,49 +172,65 @@ a ?? (b && c && d);

If you would like to ignore expressions containing operands of certain primitive types that can be falsy then you may pass an object containing a boolean value for each primitive:

- `string: true`, ignores `null` or `undefined` unions with `string` (default: false).
- `number: true`, ignores `null` or `undefined` unions with `number` (default: false).
- `bigint: true`, ignores `null` or `undefined` unions with `bigint` (default: false).
- `boolean: true`, ignores `null` or `undefined` unions with `boolean` (default: false).
- `string: true`, ignores `null` or `undefined` unions with `string` (default:`false`).
- `number: true`, ignores `null` or `undefined` unions with `number` (default:`false`).
- `bigint: true`, ignores `null` or `undefined` unions with `bigint` (default:`false`).
- `boolean: true`, ignores `null` or `undefined` unions with `boolean` (default:`false`).

Incorrect code for `ignorePrimitives: { string: false }`, and correct code for `ignorePrimitives: { string: true }`:
Examples of code for this rule with `{ ignorePrimitives: { string: false } }`:

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "ignorePrimitives": { "string": false } }'
declare const foo: string | undefined;

```ts option='{ "ignorePrimitives": { "string": true } }' showPlaygroundButton
const foo: string | undefined = 'bar';
foo || 'a string';
```

Correct code for both `ignorePrimitives: { string: false }` and `ignorePrimitives: { string: true }`:
</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "ignorePrimitives": { "string": false } }'
declare const foo: string | undefined;

```ts option='{ "ignorePrimitives": { "string": true } }' showPlaygroundButton
const foo: string | undefined = 'bar';
foo ?? 'a string';
```

</TabItem>
</Tabs>

Also, if you would like to ignore all primitives types, you can set `ignorePrimitives: true`. It is equivalent to `ignorePrimitives: { string: true, number: true, bigint: true, boolean: true }`.

### `ignoreBooleanCoercion`

{/* insert option description */}

Incorrect code for `ignoreBooleanCoercion: false`, and correct code for `ignoreBooleanCoercion: true`:
Examples of code for this rule with `{ ignoreBooleanCoercion: false }`:

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "ignoreBooleanCoercion":true }' showPlaygroundButton
let a: string | true | undefined;
let b: string | boolean | undefined;
```ts option='{ "ignoreBooleanCoercion":false }'
declare const a: string | true | undefined;
declare const b: string | boolean | undefined;

const x = Boolean(a || b);
```

Correct code for `ignoreBooleanCoercion: false`:
</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "ignoreBooleanCoercion": false }' showPlaygroundButton
let a: string | true | undefined;
let b: string | boolean | undefined;
```ts option='{ "ignoreBooleanCoercion": false }'
declare const a: string | true | undefined;
declare const b: string | boolean | undefined;

const x = Boolean(a ?? b);
```

</TabItem>
</Tabs>

### `allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing`

:::danger Deprecated
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