Solve - flatMap is not a function Error in JavaScript

Solve - flatMap is not a function Error #

The "flatMap is not a function" error occurs for multiple reasons:

• Using the flatMap method in a browser that doesn't support it.
• Using the flatMap method on a value that is not an array.

Here is an example of how the error occurs.

Copied!
const arr = {};

// ⛔️ TypeError: arr.flatMap is not a function
const result = arr.flatMap(str => str.split(' '));

We called the Array.flatMap() method on an object and got the error back.

To solve the "flatMap is not a function" error, make sure to only call the flatMap method on arrays and in browsers that support it. The flatMap method returns a new array where each element is the result of the callback function flattened to a depth of 1.

Copied!
const arr = ['one two', 'three four'];

const result = arr.flatMap(str => str.split(' '));

// 👇️ ['one', 'two', 'three', 'four']
console.log(result);

Copied!
// ✅ Supported in Internet Explorer
const arr = ['one two', 'three four'];

const result = arr.reduce((acc, curr) => acc.concat(curr.split(' ')), []);

// 👇️ ['one', 'two', 'three', 'four']
console.log(result);

You can conditionally check if the value is an array by using the Array.isArray method.

Copied!
const arr = null;

const result = Array.isArray(arr) ? arr.flatMap(str => str.split(' ')) : [];

console.log(result); // 👉️ []

We used a ternary operator, which is very similar to an if/else statement.

If the value is an array, we return the result of calling the flatMap method on it, otherwise we return an empty array. This way, you won't get an error, even if the value is not an array.

If you have an array-like object which you're trying to convert to an array before calling the flatMap method, use the Array.from method.

Copied!
const set = new Set(['one two', 'three four']);

const result = Array.from(set).flatMap(str => str.split(' '));
console.log(result); // 👉️ ['one', 'two', 'three', 'four']

Before calling the flatMap method, we convert the value to an array.

You could also use the spread syntax (...) to achieve the same result.

Copied!
const set = new Set(['one two', 'three four']);

const result = [...set].flatMap(str => str.split(' ');
console.log(result); // 👉️ ['one', 'two', 'three', 'four']

If the error persists, console.log the value you're calling the flatMap method on and make sure it's a valid array.