How to solve reduce is not a function error in JavaScript

In this tutorial, we are going to learn about how to solve the TypeError: reduce is not a function in JavaScript

When we use a Array.reduce() method on a value which is not an data type other than array we will get the following error in our console.

Example:

const arr =  {a: 1, b: 2};

arr.reduce((result, current) => result+current);

Output:

"TypeError: arr.reduce is not a function

In the example above, we are getting the error because we using the reduce() method on a data type object.

To solve the error, we need to make sure to call the reduce() method on a data type array or convert it to an array before calling a reduce method on it.

Here is an example:

const arr = [1 ,2];
const sum = arr.reduce((result, current) => result + current));

console.log(sum);

Output:

3

Note: The reduce() method adds the all elements in an array and return the sum of it.

We can also check, if the given value is a data type array or not before calling the reduce() method on it. So that, we can avoid the runtime errors.

var arr = [1, 2, 3];

if(Array.isArray(arr)){
    arr.reduce((result, current) => result + current);
}else{
    console.log("Given data is not an array")
}

In the above example: Array.isArray() takes the variable as an argument and returns true if the given variable is a valid array otherwise it will return false.

Conclusion

The “reduce is not a function” error occurs, when we call a reduce() method on a value which is not an array. To solve the error, make sure to use reduce() method on a valid arrays or convert the values to an array before calling the reduce() method.