The missing js and ts helpers

Arrays

• sum: Calculates the sum of an array of numbers. Returns 0 if the array is empty.

sum([1,2,3]) // 6

• mean: Computes the mean of an array of number. Returns 0 if the array is empty

mean([1,2,3]) // 2

• findIndexAndValue: Finds a value in an array given a predicate, and returns an object with the value and its index

const fruits = ["banana", "peach", "strawberry"	];

findIndexAndValue(fruits, (f) => f === "peach") // {index: 1, value: "peach"}

• range: Creates an array of numbers between start (defaults to 0) and stop (excluded) in increments of step (defaults to 1)

range(3) // [0,1,2]
range(1,3) // [1,2]
range(1,6,2) // [1,3,5]

Functions

• once: Decorator making a function callable once

let i = 0;

const increment = () => i++;
const wrapped = once(increment);

wrapped(); // i = 1
wrapped(); // i = 1
wrapped(); // i = 1

Heap

A fast priority queue / heap implementation, with O(nlog(n)) complexity.

The constructor takes a comparator function.

Public fields:

• size: (number) the size of the heap
• isEmpty: (boolean) whether the heap is empty
• enqueue: adds an element to the queue and prioritizes it
• dequeue: pops the next element in the priority queue
• peek: look at the next element without popping it
• has: checks whether a given element is in the queue

const queue = new PriorityQueue((a: string, b: string) => a < b ? -1 : a === b ? 0 : 1);

queue.enqueue("Bob");
queue.enqueue("Zack");
queue.enqueue("Alice");

queue.size(); // 3
queue.has("Dan"); // false

queue.dequeue(); // Alice
queue.dequeue(); // Bob

queue.peek(); // Zack
queue.isEmpty(); // false

queue.dequeue(); // Zack

Numbers

• round(value: number, decimalPlaces = 0): Rounds value toa precision of decimalPlaces. By default returns value rounded to the nearest integer

round(Math.PI, 2) // 3.14

• modulo(n: number, d: number): Computes n modulo d. Note: the modulo operator has the same sign as the divisor d whereas the remainder n % d has the same sign as the dividend n

modulo(-1, 3); // 2
-1 % 3;  // -1

Objects

Promises

• debounce: A debounce decorator. Parameters:
  • func The function to debounce.
  • delay (default: 100) Minimum delay in ms between calls.
  • throttle (default: false) When debouncing every new call to func resets the delay timer. When throttling the function ensures there is at least delay ms between calls

const arr = [];

const fn = debounce(() => arr.push(Math.random()), 10);

fn();
await sleep(6);
fn();
await sleep(6);
fn();
await sleep(11);

arr.length; // 1

• Debounce: a debounce class, similar to the simpler function, but with the ability to flush

Random

• randint(a:number, b: number): Returns a random integer in [a;b]

randint(0, 5) // 2

Sets

• areSetsEqual: checks whether two sets are equal

const s1 = new Set([2, 3, 4]);
const s2 = new Set([4, 3, 2]);

areSetsEqual(s1, s2); // true

Strings

• randomString: Creates a random string of a given length in the alphabet [a-zA-Z0-9_-] (64 characters)

randomString(8); // TNxOLDho

• nanoId: A fast alias of randomString with length = 8 by default

nanoId(); // b6eKfYLB

• capitalize: Turns the first letter of a string to uppercase

capitalize("capitalized") // "Capitalized"

Types

• type: Returns a string representation of the type of an object more precise type than typeof.

// null / undefined types
type(null); // "null"
type(undefined); // "undefined"

// other primitive types
type(0); // "number"
type(BigInt(0)); // "bigint"
type(true); // "boolean"
type(""); // "string"
type(Symbol("")); // "symbol"

// object types
type([]); // "array"
type(new Date()); // "date"
type(new Boolean(true)); // "boolean"
type(new Number(0)); // "number"
type(new String("")); // "string"
type(new Error("")); // "error"
type(new RegExp("a")); // "regexp"
type(/a/); // "regexp"
type({}); // "object"

// function type
type(() => 1); // "function"
type(class Dog {}); // "class"

• StrictOmit<T, K extends keyof T>: Utility type similar to Omit with constrained keys for stricter types.

• StrictExtract<T, U extends T>: Utility type similar to Extract with constrained keys for stricter types

• Timeout: Return type of setTimeout