Solution To Fix The Error “TypeError: flatMap Is Not A Function” In JavaScript

TypeError: flatMap is not a function in JavaScript is an error that is not complex to fix. In this article, I will give some reasons why your program throws the above error and give you the best solution.

Why does the TypeError: flatMap is not a function in JavaScript happen?

There are many reasons for your program to output a TypeError: flatMap is not a function in JavaScript error, but the most common are:

• Call the flatMap() method from a value that is not an array.
• Browsers don’t understand the flatMap() method.

The error message occurs as follows:

Uncaught TypeError: flatMap is not a function

Example:

var num = 184301; // => Number
var result = num.flatMap((x) => x - 1);
console.log(result);

Output:

Uncaught TypeError: flatMap is not a function

I used a number to call the flatMap() method, and this time my program returned the error line “Uncaught TypeError: flatMap is not a function”.

How to fix TypeError: flatMap is not a function in JavaScript?

Before fixing this error, we need to understand the flatMap() method to find the most reasonable way to solve this error.

flatMap() method

Syntax:

flatMap((element, index, array) => { /* … */ });

Parameters:

• element is the element of the array being processed by the method.
• index is the address of the element the method is processing.
• array is the array that was called.

flatMap() method is a combination of the map() and flat() methods. It is often used in the case of using map() in combination with the flat() method with a depth of flat() of 1.

After understanding the flatMap() method, I will give some solutions to fix the error on a case-by-case basis below.

Call the flatMap() method from a value that is not an array

When your program throws the error “Uncaught TypeError: flatMap is not a function”, check whether the variable calling flatMap() method has a value type of array first. If not, this error occurs because of calling the flatMap() method from a value, not an array.

To ensure this is not the case, you should check the variable first to see if it has an array value and then use that variable to call the method. Do it like the following example:

Example:

var arr = ["Hello I", "am", "LearnShareIT"]; // => Array

// Check if arr is an array
if (Array.isArray(arr)) {
console.log(arr.flatMap((x) => x.split(" ")));
} else {
console.log("This is not an array");
}

Output:

(4) ['Hello', 'I', 'am', 'LearnShareIT']

Example:

var arr = 1243565; // => Number

// Check if arr is an array
if (Array.isArray(arr)) {
console.log(arr.flatMap((x) => x.split(" ")));
} else {
console.log("This is not an array");
}

Output:

This is not an array

When we use conditional statements to check, we will ensure that the above error will not be thrown again. Before using the flatMap() method, remember that it only works when the variable calling it is an array.

Browser does not understand the flatMap() method

Suppose you use Internet Explorer to load your page using the flatMap() method. In that case, you will get an “Uncaught TypeError: flatMap is not a function” error because Internet Explorer does not understand this method.

At this point, we will have to find a way to replace the flatMap() method with another similar piece of code, and I did it like this:

var arr = ["Hello I", "am", "LearnShareIT"]; // => Array

// Check if arr is an array
if (Array.isArray(arr)) {
console.log(arr.map((x) => x.split(" ")).flat());
} else {
console.log("This is not an array");
}

Output:

(4) ['Hello', 'I', 'am', 'LearnShareIT']

As I have mentioned, the flatMap() method is a combination of the map() and flat() methods, so when the flatMap() method cannot be used, it can be replaced manually by using a combination of the map() and flat( ) methods together.

Summary

In this article, I have showed you the ways to handle the TypeError: flatMap is not a function in JavaScript in two cases when calling the flatMap() method from a value that is not an array, the browser does not understand the flatMap() method. It will help you understand it without worrying about getting this error. I hope this article helps you and your program. Good luck.

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