JavaScript Array forEach Loop: Complete Tutorial

Master the JavaScript forEach() method for iterating arrays without creating new output. Covers syntax, callback parameters, real-world iteration patterns, comparison with for loops, limitations, and common mistakes.

JavaScriptbeginner

RuneHub Team

February 27, 2026

13 min read

RuneHub Team

Feb 27, 2026

13 min read

The forEach() method executes a function once for every element in an array. Unlike map() or filter(), it does not return a new array. It simply runs your callback on each element and returns undefined. This makes forEach() the right tool when you need to perform side effects (logging, DOM updates, API calls) for every item without building a new collection.

What forEach() Does

forEach() visits every element in order and passes it to a callback function. There is no return value and no way to stop early:

javascript

const fruits = ["apple", "banana", "cherry", "date"];
 
fruits.forEach(function (fruit) {
  console.log(fruit.toUpperCase());
});
// APPLE
// BANANA
// CHERRY
// DATE

Syntax

javascript

array.forEach(callback(element, index, array), thisArg)

Parameter	Description
`element`	The current element being processed
`index`	Index of the current element (optional)
`array`	The original array (optional)
`thisArg`	Value to use as `this` inside the callback (optional)

Return Value

Always undefined. If you need a new array, use map(). If you need a single accumulated value, use reduce().

Basic Examples

Using All Three Callback Parameters

javascript

const colors = ["red", "green", "blue"];
 
colors.forEach((color, index, arr) => {
  const isLast = index === arr.length - 1;
  console.log(`${index + 1}/${arr.length}: ${color}${isLast ? " (last)" : ""}`);
});
// 1/3: red
// 2/3: green
// 3/3: blue (last)

Logging Table Rows

javascript

const employees = [
  { name: "Alice", department: "Engineering", salary: 95000 },
  { name: "Bob", department: "Marketing", salary: 72000 },
  { name: "Carol", department: "Engineering", salary: 110000 },
];
 
employees.forEach(emp => {
  console.log(`${emp.name.padEnd(10)} ${emp.department.padEnd(15)} $${emp.salary}`);
});
// Alice      Engineering     $95000
// Bob        Marketing       $72000
// Carol      Engineering     $110000

Updating Object Properties in Place

javascript

const tasks = [
  { id: 1, title: "Write tests", completed: false },
  { id: 2, title: "Fix bug #42", completed: false },
  { id: 3, title: "Deploy v2", completed: false },
];
 
tasks.forEach(task => {
  task.completed = true;
  task.completedAt = new Date().toISOString();
});
 
console.log(tasks[0].completed); // true
console.log(tasks[0].completedAt); // "2026-03-05T..."

Mutations Are Visible

Because objects are passed by reference, changes made inside forEach() affect the original array's objects. This is intentional when you need to update records in place, but it can be surprising if you expect immutability.

Real-World Patterns

Sending Batch Notifications

javascript

const subscribers = [
  { email: "alice@example.com", name: "Alice" },
  { email: "bob@example.com", name: "Bob" },
  { email: "carol@example.com", name: "Carol" },
];
 
subscribers.forEach(subscriber => {
  sendEmail({
    to: subscriber.email,
    subject: "Weekly Digest",
    body: `Hi ${subscriber.name}, here's your weekly update.`,
  });
  console.log(`Sent to ${subscriber.email}`);
});

Populating a Map from Array Data

javascript

const rawProducts = [
  { sku: "KB-001", name: "Mechanical Keyboard", price: 129.99 },
  { sku: "MS-002", name: "Wireless Mouse", price: 49.99 },
  { sku: "HD-003", name: "USB-C Hub", price: 39.99 },
];
 
const productMap = new Map();
rawProducts.forEach(product => {
  productMap.set(product.sku, product);
});
 
console.log(productMap.get("MS-002").name); // "Wireless Mouse"

Accumulating Side Effects with Index

javascript

const steps = [
  "Clone the repository",
  "Install dependencies",
  "Configure environment variables",
  "Run database migrations",
  "Start the development server",
];
 
const instructions = [];
steps.forEach((step, index) => {
  instructions.push(`Step ${index + 1}: ${step}`);
});
 
console.log(instructions.join("\n"));

forEach() Cannot Be Stopped Early

This is the most important limitation. You cannot use break, continue, or return to exit early from forEach():

javascript

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
 
// return only exits the CURRENT callback invocation, not the loop
numbers.forEach(n => {
  if (n > 5) return; // Does NOT stop forEach. Just skips this callback run.
  console.log(n);
});
// 1, 2, 3, 4, 5 (logs these, but forEach still runs for 6-10)

If you need to stop early, use a for loop with break, or use find() / some() which stop at the first match:

javascript

// for loop: stops at first match
for (let i = 0; i < numbers.length; i++) {
  if (numbers[i] > 5) break;
  console.log(numbers[i]);
}
 
// some(): stops when callback returns true
numbers.some(n => {
  if (n > 5) return true; // Stops iteration
  console.log(n);
  return false;
});

No Break in forEach

Throwing an exception is the only way to actually halt forEach(), and that is an anti-pattern. If you need early termination, use a for loop, for...of loop, some(), every(), or find() instead.

forEach() vs for Loop

Feature	forEach()	for loop
Early exit (break)	Not supported	Supported
Skip iteration (continue)	Use `return` (skips callback)	Use `continue`
Return value	`undefined`	N/A
Access to index	Via second callback parameter	Loop variable `i`
Async/await support	Does not wait for promises	Works with `await` in loop body
Readability	Higher for simple iteration	Better for complex control flow
Performance	Marginally slower (function call overhead)	Marginally faster

Async Pitfall

forEach() fires all callbacks synchronously and does not await promises:

javascript

const urls = ["/api/user/1", "/api/user/2", "/api/user/3"];
 
// Bug: forEach does NOT await. All fetches fire at once, results are lost.
urls.forEach(async url => {
  const response = await fetch(url);
  const data = await response.json();
  console.log(data); // Logs in unpredictable order
});
console.log("Done"); // Logs BEFORE any fetch completes
 
// Fix: use for...of for sequential async
for (const url of urls) {
  const response = await fetch(url);
  const data = await response.json();
  console.log(data); // Sequential, predictable order
}
console.log("Done"); // Logs AFTER all fetches

forEach() Skips Empty Slots

Sparse arrays (created with delete or literal holes) have empty slots that forEach() skips entirely:

javascript

const sparse = [1, , 3, , 5]; // Holes at index 1 and 3
 
sparse.forEach((value, index) => {
  console.log(`Index ${index}: ${value}`);
});
// Index 0: 1
// Index 2: 3
// Index 4: 5
// (indices 1 and 3 are skipped, not logged as undefined)

This is different from undefined values, which ARE visited:

javascript

const withUndefined = [1, undefined, 3, undefined, 5];
 
withUndefined.forEach((value, index) => {
  console.log(`Index ${index}: ${value}`);
});
// Index 0: 1
// Index 1: undefined
// Index 2: 3
// Index 3: undefined
// Index 4: 5

Common Mistakes

Trying to return a value from forEach():

javascript

const numbers = [1, 2, 3, 4, 5];
 
// Bug: forEach always returns undefined
const doubled = numbers.forEach(n => n * 2);
console.log(doubled); // undefined
 
// Fix: use map() when you need a new array
const doubled2 = numbers.map(n => n * 2);
console.log(doubled2); // [2, 4, 6, 8, 10]

Expecting break to work:

javascript

const items = ["a", "b", "c", "d"];
 
// SyntaxError: break is not valid inside a callback function
// items.forEach(item => {
//   if (item === "c") break; // SyntaxError
// });
 
// Fix: use for...of
for (const item of items) {
  if (item === "c") break;
  console.log(item);
}

Using forEach() for async operations:

javascript

const ids = [1, 2, 3];
 
// Bug: forEach does not await promises
ids.forEach(async id => {
  const user = await fetchUser(id);
  console.log(user.name);
});
// "All done" logs before any user is fetched
console.log("All done");
 
// Fix: use for...of with await
async function loadUsers() {
  for (const id of ids) {
    const user = await fetchUser(id);
    console.log(user.name);
  }
  console.log("All done"); // Now truly done
}

Best Practices

Use forEach() only for side effects. If you need a new array, use map(). If you need a single value, use reduce().
Choose for...of when you need early exit or async/await. forEach() cannot break or properly handle promises.
Keep callbacks small. If the callback body exceeds 10 lines, extract it into a named function for readability.
Do not chain after forEach(). Since it returns undefined, any method chained after it (like .map()) will throw.
Use arrow functions for concise callbacks: arr.forEach(item => console.log(item)) is clean and readable.

Rune AI

Key Insights

Side effects only: forEach() returns undefined; use map() or filter() when you need a new array
No early exit: break and continue do not work; return only skips the current callback
Async pitfall: forEach() does not await promises; use for...of for sequential async operations
Skips empty slots: sparse array holes are ignored, but explicit undefined values are visited
Keep it simple: extract long callbacks into named functions for clarity

Frequently Asked Questions

Does forEach() modify the original array?

forEach() itself does not modify the array. However, your callback can modify objects within the array because objects are passed by reference. If you reassign the element parameter inside the callback, it has no effect on the original array. Modifying properties of objects, on the other hand, changes them everywhere.

Can I use break or continue inside forEach()?

No. `break` and `continue` are loop statements and cause a SyntaxError inside a callback function. You can use `return` to skip the rest of the current iteration (similar to `continue`), but there is no way to stop forEach() early. Use a for loop or for...of when you need break/continue behavior.

What is the difference between forEach() and map()?

forEach() runs a callback on every element and returns `undefined`. map() runs a callback on every element and returns a new array with the results. Use forEach() for side effects (logging, mutations, API calls). Use map() when you need to transform data into a new array.

Does forEach() work on objects?

forEach() is an array method. Plain objects do not have it. To iterate over an object's keys, use `Object.keys(obj).forEach()`, `Object.entries(obj).forEach()`, or a `for...in` loop.

Is forEach() slower than a for loop?

In practice, the difference is negligible for most applications. forEach() has a marginal overhead from calling a function per element, but modern JavaScript engines optimize this heavily. Choose based on readability and requirements (early exit, async), not micro-performance.

Conclusion

The forEach() method is JavaScript's most straightforward tool for running a side-effect function on every element of an array. It excels at logging, DOM updates, batch mutations, and any operation where you process items without building a new collection. Its two critical limitations are the inability to exit early (no break) and the lack of proper async/await support. When either limitation applies, a for loop or for...of is the better choice, and when you need a new array, map() is the right fit.

JavaScript Array forEach Loop: Complete Tutorial

What forEach() Does

Syntax

Return Value

Basic Examples

Using All Three Callback Parameters

Logging Table Rows

Updating Object Properties in Place

Mutations Are Visible

Real-World Patterns

Sending Batch Notifications

Populating a Map from Array Data

Accumulating Side Effects with Index

forEach() Cannot Be Stopped Early

No Break in forEach

forEach() vs for Loop

Async Pitfall

forEach() Skips Empty Slots

Common Mistakes

Best Practices

Rune AI

Frequently Asked Questions

Does forEach() modify the original array?

Can I use break or continue inside forEach()?

What is the difference between forEach() and map()?

Does forEach() work on objects?

Is forEach() slower than a for loop?

Conclusion

Tags

More in this topic

OffscreenCanvas API in JS for UI Performance

Advanced Web Workers for High Performance JS

JavaScript Macros and Abstract Code Generation

JavaScript Array forEach Loop: Complete Tutorial

What forEach() Does

Syntax

Return Value

Basic Examples

Using All Three Callback Parameters

Logging Table Rows

Updating Object Properties in Place

Mutations Are Visible

Real-World Patterns

Sending Batch Notifications

Populating a Map from Array Data

Accumulating Side Effects with Index

forEach() Cannot Be Stopped Early

No Break in forEach

forEach() vs for Loop

Async Pitfall

forEach() Skips Empty Slots

Common Mistakes

Best Practices

Rune AI

Frequently Asked Questions

Does forEach() modify the original array?

Can I use break or continue inside forEach()?

What is the difference between forEach() and map()?

Does forEach() work on objects?

Is forEach() slower than a for loop?

Conclusion

Tags

More in this topic

OffscreenCanvas API in JS for UI Performance

Advanced Web Workers for High Performance JS

JavaScript Macros and Abstract Code Generation