Solve - reduce is not a function Error in JavaScript

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Borislav Hadzhiev

Wed Oct 20 20212 min read

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Solve - reduce is not a function Error #

The "reduce is not a function" error occurs when we call the reduce() method on a value that is not an array. To solve the error, make sure to only call the reduce method on arrays or conditionally check if the value is an array before calling the method.

typeerror reduce is not a function

Here is an example of how the error occurs.

index.js
const arr = {}; // โ›”๏ธ TypeError: arr.reduce is not a function const result = arr.reduce((acc, curr) => acc + curr, 0);

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

To solve the error, console.log the value you're calling the reduce method on and make sure it's a valid array.

index.js
const arr = [1, 2, 3]; const result = arr.reduce((acc, curr) => acc + curr, 0); console.log(result); // ๐Ÿ‘‰๏ธ 6

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

index.js
const arr = null; const result = Array.isArray(arr) ? arr.reduce((acc, curr) => acc + curr, 0) : 0; console.log(result); // ๐Ÿ‘‰๏ธ 0

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 reduce method on it, otherwise we return 0. This way, you won't get an error, even if the value is not an array.

If the value is fetched from a remote server, make sure it is of the type you expect it to be by logging it to the console and make sure you have parsed it to a native JavaScript array before calling the reduce method on it.

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

index.js
const set = new Set([1, 2, 3]); const result = Array.from(set).reduce((acc, curr) => acc + curr, 0); console.log(result); // ๐Ÿ‘‰๏ธ 6

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

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

index.js
const set = new Set([1, 2, 3]); const result = [...set].reduce((acc, curr) => acc + curr, 0); console.log(result); // ๐Ÿ‘‰๏ธ 6

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