forEach (for Maps)

Executes a provided function once for each entry in a Map.

forEach(map, callback);

INFO

This function is available exclusively from es-toolkit/map to avoid potential conflicts with similar functions for other collection types.

Usage

forEach(map, callback)

Use forEach when you want to execute a function for each entry in a Map. The callback function receives the value, key, and the Map itself as arguments. This is useful for side effects like logging, updating external state, or performing operations on each entry.

import { forEach } from 'es-toolkit/map';

const map = new Map([
  ['a', 1],
  ['b', 2],
  ['c', 3],
]);

forEach(map, (value, key) => {
  console.log(`${key}: ${value}`);
});
// Output:
// a: 1
// b: 2
// c: 3

You can perform various operations on each entry.

import { forEach } from 'es-toolkit/map';

// Accumulate values
const prices = new Map([
  ['apple', 1.5],
  ['banana', 0.75],
  ['orange', 2.0],
]);

let total = 0;
forEach(prices, value => {
  total += value;
});
// total is now 4.25

// Collect entries into an array
const users = new Map([
  ['user1', { name: 'Alice', age: 25 }],
  ['user2', { name: 'Bob', age: 30 }],
]);

const userList: string[] = [];
forEach(users, (value, key) => {
  userList.push(`${key}: ${value.name} (${value.age})`);
});
// userList: ['user1: Alice (25)', 'user2: Bob (30)']

// Update external Map based on conditions
const inventory = new Map([
  ['item1', { stock: 10, price: 5 }],
  ['item2', { stock: 0, price: 10 }],
  ['item3', { stock: 5, price: 15 }],
]);

const outOfStock = new Map<string, any>();
forEach(inventory, (value, key) => {
  if (value.stock === 0) {
    outOfStock.set(key, value);
  }
});
// outOfStock contains item2

Parameters

• map (Map<K, V>): The Map to iterate over.
• callback ((value: V, key: K, map: Map<K, V>) => void): A function to execute for each entry.

Returns

(void): This function does not return a value.