This refactoring replaces string comparison chains with an `array.includes()` call. It works for regular string comparisons with `|| ===` and for negated string comparisons with `&& !==`. When the string comparison is negated, the `.includes` call is prefixed with `!`.

## Example

```javascript
if (obj.property === "value1" 
    || obj.property === "value2" 
    || obj.property === "value3") {
    // ...
}
```
becomes
```javascript
if (["value1", "value2", "value3"].includes(obj.property)) {
    // ...
}
```



Replace `|| value === 'aString'` and `&& value !== 'aString'`  chains with `array.includes()`.

Convert string comparison chain to array.includes()

**The optional chaining operator `.?` returns the value of an object property when the object is available and `undefined` otherwise.**
It is similar to the standard `.` chaining operator, with an added check if the object is defined (i.e., not [nullish](https://developer.mozilla.org/en-US/docs/Glossary/Nullish)).

The optional chaining operator lets you **write concise and safe chains of connected objects** when some of those objects can be `null` or `undefined`. Before the introduction of optional chaining in ES2020, the `&&` operator was often used to check if an object is available (`obj && obj.value`).

You can often simplify existing checks with the optional chaining pattern:
- `obj && obj.property` becomes `obj?.property`
- `obj != null && obj.property` becomes `obj?.property`
- `obj != null ? obj.property : undefined` becomes `obj?.property`
- `arr && arr[i]` becomes `arr?.[i]`
- `f && f()` becomes `f?.()`
- etc.


Replace various guard expressions with the optional chaining operator (`?.`).

Convert to optional chaining

The flip operator refactoring exchanges a binary expression's left and right operand. When necessary, it updates the operator, e.g., when changing from `a < b` to `b > a`.

Swap the left and right operands and update the operator if necessary.

Flip operator

### Why is this useful?
Negated expressions take more cognitive effort to reason about than regular expressions. Inverting negated conditions can remove unnecessary complexity. One exception is nullish comparisons where, for example, `!= null` indicates the existence of a value.

### Mechanics
The condition of the if statement or conditional expression is negated. The then and else blocks or expressions are exchanged.

Negate the condition of an if-statement or conditional expression and swap its content.

Invert condition

### Why is this refactoring helpful?
Pulling a negation out of an expression can be part of a larger refactoring, e.g. when moving the negation to a different location in the code.

Move the not-operator (`!`) out of a binary expression.

Pull up negation

### Why is this refactoring helpful?
Push negation into an expression can simplify code, either directly or by enabling the [removal of double negation](/documentation/code-assist/remove-double-negation).

Push the not-operator (`!`) into an expression and negate it.

Push down negation

### Why is this refactoring helpful?
Removing an unnecessary double negation simplifies the code.

Remove double negation (`!!`) expressions.

Remove double negation

Replace binary expression with a more straightforward equivalent expression.

Simplify binary expression

The `== null` check is a concise expression to identify nullish values (`null` and `undefined`).

This refactoring replaces the following combinations of longer strict equality checks with the shorter `null` comparison:

- `a === null || a === undefined` becomes `a == null`
- `b !== null && b !== undefined` becomes `b != null`
- `x.f(1, 2) === null || x.f(1, 2) === undefined` becomes `x.f(1, 2) == null`


Replace different nullish checks with `== null`.

Use == null comparison

Boolean logic can be challenging to read, especially as expressions get more complex. The JavaScript Assistant provides several refactorings that can help you simplify and tease apart logical expressions to make them easier to understand:

9 Code Assists for Logical Expressions