Upgrade TypeScript (#102)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

Author: bobjflong

package.json

@@ -48,20 +48,20 @@
 		"@sindresorhus/tsconfig": "^0.6.0",
 		"@types/benchmark": "^1.0.31",
 		"@types/node": "^12.12.7",
-		"@typescript-eslint/eslint-plugin": "^1.11.0",
-		"@typescript-eslint/parser": "^1.11.0",
+		"@typescript-eslint/eslint-plugin": "^2.25.0",
+		"@typescript-eslint/parser": "^2.25.0",
 		"ava": "^2.0.0",
 		"benchmark": "^2.1.4",
 		"codecov": "^3.3.0",
 		"del-cli": "^3.0.0",
 		"delay": "^4.2.0",
-		"eslint-config-xo-typescript": "^0.16.0",
+		"eslint-config-xo-typescript": "^0.27.0",
 		"in-range": "^2.0.0",
 		"nyc": "^14.0.0",
 		"random-int": "^2.0.0",
 		"time-span": "^3.1.0",
 		"ts-node": "^8.3.0",
-		"typescript": "3.7.2",
+		"typescript": "3.8.3",
 		"xo": "^0.25.3"
 	},
 	"ava": {

source/index.ts

@@ -10,6 +10,7 @@ type Task<TaskResultType> =
 	| (() => PromiseLike<TaskResultType>)
 	| (() => TaskResultType);
 
+// eslint-disable-next-line @typescript-eslint/no-empty-function
 const empty = (): void => {};
 
 const timeoutError = new TimeoutError();
@@ -56,7 +57,7 @@ export default class PQueue<QueueType extends Queue<RunFunction, EnqueueOptionsT
 	constructor(options?: Options<QueueType, EnqueueOptionsType>) {
 		super();
 
-		// eslint-disable-next-line @typescript-eslint/no-object-literal-type-assertion
+		// eslint-disable-next-line @typescript-eslint/consistent-type-assertions
 		options = {
 			carryoverConcurrencyCount: false,
 			intervalCap: Infinity,
@@ -65,15 +66,14 @@ export default class PQueue<QueueType extends Queue<RunFunction, EnqueueOptionsT
 			autoStart: true,
 			queueClass: PriorityQueue,
 			...options
-		// TODO: Remove this `as`.
 		} as Options<QueueType, EnqueueOptionsType>;
 
 		if (!(typeof options.intervalCap === 'number' && options.intervalCap >= 1)) {
-			throw new TypeError(`Expected \`intervalCap\` to be a number from 1 and up, got \`${options.intervalCap}\` (${typeof options.intervalCap})`);
+			throw new TypeError(`Expected \`intervalCap\` to be a number from 1 and up, got \`${options.intervalCap?.toString() ?? ''}\` (${typeof options.intervalCap})`);
 		}
 
 		if (options.interval === undefined || !(Number.isFinite(options.interval) && options.interval >= 0)) {
-			throw new TypeError(`Expected \`interval\` to be a finite number >= 0, got \`${options.interval}\` (${typeof options.interval})`);
+			throw new TypeError(`Expected \`interval\` to be a finite number >= 0, got \`${options.interval?.toString() ?? ''}\` (${typeof options.interval})`);
 		}
 
 		this._carryoverConcurrencyCount = options.carryoverConcurrencyCount!;
@@ -226,6 +226,7 @@ export default class PQueue<QueueType extends Queue<RunFunction, EnqueueOptionsT
 	/**
 	Adds a sync or async task to the queue. Always returns a promise.
 	*/
+	// eslint-disable-next-line @typescript-eslint/prefer-readonly-parameter-types
 	async add<TaskResultType>(fn: Task<TaskResultType>, options: Partial<EnqueueOptionsType> = {}): Promise<TaskResultType> {
 		return new Promise<TaskResultType>((resolve, reject) => {
 			const run = async (): Promise<void> => {
@@ -349,7 +350,7 @@ export default class PQueue<QueueType extends Queue<RunFunction, EnqueueOptionsT
 
 	For example, this can be used to find the number of items remaining in the queue with a specific priority level.
 	*/
-	sizeBy(options: Partial<EnqueueOptionsType>): number {
+	sizeBy(options: Readonly<Partial<EnqueueOptionsType>>): number {
 		return this._queue.filter(options).length;
 	}
 

source/priority-queue.ts

@@ -25,17 +25,22 @@ export default class PriorityQueue implements Queue<RunFunction, PriorityQueueOp
 			return;
 		}
 
-		const index = lowerBound(this._queue, element, (a, b) => b.priority! - a.priority!);
+		const index = lowerBound(
+			this._queue, element,
+			(a: Readonly<PriorityQueueOptions>, b: Readonly<PriorityQueueOptions>) => b.priority! - a.priority!
+		);
 		this._queue.splice(index, 0, element);
 	}
 
 	dequeue(): RunFunction | undefined {
 		const item = this._queue.shift();
-		return item && item.run;
+		return item?.run;
 	}
 
-	filter(options: Partial<PriorityQueueOptions>): RunFunction[] {
-		return this._queue.filter(element => element.priority === options.priority).map(element => element.run);
+	filter(options: Readonly<Partial<PriorityQueueOptions>>): RunFunction[] {
+		return this._queue.filter(
+			(element: Readonly<PriorityQueueOptions>) => element.priority === options.priority
+		).map((element: Readonly<{ run: RunFunction }>) => element.run);
 	}
 
 	get size(): number {