arrayEmptyCallbackSlots

Reports array methods with callbacks that will never be invoked on arrays with empty slots.

✅ This rule is included in the ts logical and logicalStrict presets.

When the Array constructor is called with a single number argument, it creates an array with the specified number of empty slots (not actual undefined values). Callback methods like map, filter, forEach, and others skip empty slots, so callbacks passed to these methods will never be invoked.

This rule reports when array methods with callbacks are called on arrays created with new Array(n).

new 
var Array: ArrayConstructor
new (arrayLength?: number) => any[] (+2 overloads)
Array(5).
Array<any>.map<number>(callbackfn: (value: any, index: number, array: any[]) => number, thisArg?: any): number[]
Calls a defined callback function on each element of an array, and returns an array that contains the results.
@param ― callbackfn A function that accepts up to three arguments. The map method calls the callbackfn function one time for each element in the array.
@param ― thisArg An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.
map((
_: any
_) => 0);

new 
var Array: ArrayConstructor
new (arrayLength?: number) => any[] (+2 overloads)
Array(10).
Array<any>.filter(predicate: (value: any, index: number, array: any[]) => unknown, thisArg?: any): any[] (+1 overload)
Returns the elements of an array that meet the condition specified in a callback function.
@param ― predicate A function that accepts up to three arguments. The filter method calls the predicate function one time for each element in the array.
@param ― thisArg An object to which the this keyword can refer in the predicate function. If thisArg is omitted, undefined is used as the this value.
filter((
value: any
value) => 
value: any
value > 0);

new 
var Array: ArrayConstructor
new (arrayLength?: number) => any[] (+2 overloads)
Array(3).
Array<any>.forEach(callbackfn: (value: any, index: number, array: any[]) => void, thisArg?: any): void
Performs the specified action for each element in an array.
@param ― callbackfn A function that accepts up to three arguments. forEach calls the callbackfn function one time for each element in the array.
@param ― thisArg An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.
forEach((
item: any
item) => 
var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:

A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.

Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(
item: any
item));

new 
var Array: ArrayConstructor
new (arrayLength?: number) => any[] (+2 overloads)
Array(5).
Array<any>.every(predicate: (value: any, index: number, array: any[]) => unknown, thisArg?: any): boolean (+1 overload)
Determines whether all the members of an array satisfy the specified test.
@param ― predicate A function that accepts up to three arguments. The every method calls
the predicate function for each element in the array until the predicate returns a value
which is coercible to the Boolean value false, or until the end of the array.
@param ― thisArg An object to which the this keyword can refer in the predicate function.
If thisArg is omitted, undefined is used as the this value.
every((
value: any
value) => 
value: any
value !== 
var undefined
undefined);

new 
var Array: ArrayConstructor
new (arrayLength?: number) => any[] (+2 overloads)
Array(5).
Array<any>.fill(value: any, start?: number, end?: number): any[]
Changes all array elements from start to end index to a static value and returns the modified array
@param ― value value to fill array section with
@param ― start index to start filling the array at. If start is negative, it is treated as
length+start where length is the length of the array.
@param ― end index to stop filling the array at. If end is negative, it is treated as
length+end.
fill(0).
Array<any>.map<number>(callbackfn: (value: any, index: number, array: any[]) => number, thisArg?: any): number[]
Calls a defined callback function on each element of an array, and returns an array that contains the results.
@param ― callbackfn A function that accepts up to three arguments. The map method calls the callbackfn function one time for each element in the array.
@param ― thisArg An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.
map((
_: any
_) => 1);


var Array: ArrayConstructor
Array.
ArrayConstructor.from<unknown, number>(iterable: Iterable<unknown> | ArrayLike<unknown>, mapfn: (v: unknown, k: number) => number, thisArg?: any): number[] (+3 overloads)
Creates an array from an iterable object.
@param ― iterable An iterable object to convert to an array.
@param ― mapfn A mapping function to call on every element of the array.
@param ― thisArg Value of 'this' used to invoke the mapfn.
from({ 
ArrayLike<T>.length: number
length: 5 }, (
_: unknown
_, 
index: number
index) => 
index: number
index);

new 
var Array: ArrayConstructor
new (arrayLength?: number) => any[] (+2 overloads)
Array(5).
Array<any>.fill(value: any, start?: number, end?: number): any[]
Changes all array elements from start to end index to a static value and returns the modified array
@param ― value value to fill array section with
@param ― start index to start filling the array at. If start is negative, it is treated as
length+start where length is the length of the array.
@param ― end index to stop filling the array at. If end is negative, it is treated as
length+end.
fill(
var undefined
undefined).
Array<any>.forEach(callbackfn: (value: any, index: number, array: any[]) => void, thisArg?: any): void
Performs the specified action for each element in an array.
@param ― callbackfn A function that accepts up to three arguments. forEach calls the callbackfn function one time for each element in the array.
@param ― thisArg An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.
forEach((
item: any
item) => 
var console: Console
The console module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:

A Console class with methods such as console.log(), console.error() and console.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and
process.stderr. The global console can be used without importing the node:console module.

Warning: The global console object's methods are neither consistently
synchronous like the browser APIs they resemble, nor are they consistently
asynchronous like all other Node.js streams. See the note on process I/O for
more information.
Example using the global console:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see ― source
console.
Console.log(message?: any, ...optionalParams: any[]): void (+1 overload)
Prints to stdout with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3)
(the arguments are all passed to util.format()).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format() for more information.
@since ― v0.1.100
log(
item: any
item));

[1, 2, 3].
Array<number>.map<number>(callbackfn: (value: number, index: number, array: number[]) => number, thisArg?: any): number[]
Calls a defined callback function on each element of an array, and returns an array that contains the results.
@param ― callbackfn A function that accepts up to three arguments. The map method calls the callbackfn function one time for each element in the array.
@param ― thisArg An object to which the this keyword can refer in the callbackfn function. If thisArg is omitted, undefined is used as the this value.
map((
value: number
value) => 
value: number
value * 2);

Options

This rule is not configurable.

When Not To Use It

If you intentionally use new Array(n) for its other properties (like setting length) and understand that callbacks won’t be invoked, you can disable this rule. However, this pattern is rarely intentional and usually indicates a bug.

Equivalents in Other Linters

Oxlint: oxc/uninvoked-array-callback

Made with ❤️‍🔥 around the world by the Flint team and contributors.

arrayEmptyCallbackSlots

Examples

Options

When Not To Use It

Further Reading

Equivalents in Other Linters