Borislav Hadzhiev
Reading timeยท3 min
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The "TypeError: flatMap is not a function" error occurs for two main reasons:
flatMap
method in a browser that doesn't support it.flatMap
method on a value that is not an array.Here is an example of how the error occurs.
const arr = {}; // โ๏ธ 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 "TypeError: 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.
const arr = ['one two', 'three four']; const result = arr.flatMap(str => str.split(' ')); // ๐๏ธ ['one', 'two', 'three', 'four'] console.log(result);
flatMap
method is not supported in Internet Explorer. If you have to support the browser, you can use the combination of reduce
and concat
.// โ Supported in Internet Explorer const arr = ['one two', 'three four']; const result = arr.reduce((acc, curr) => acc.concat(curr.split(' ')), []); // ๐๏ธ ['one', 'two', 'three', 'four'] console.log(result);
flatMap
directly.flatMap()
You can conditionally check if the value is an array by using the Array.isArray method.
const arr = null; const result = Array.isArray(arr) ? arr.flatMap(str => str.split(' ')) : []; console.log(result); // ๐๏ธ []
We used the 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,
otherwise, we return an empty array. This way, you won't get an error even if
the value is not an array.
You can also use a simple if
statement to achieve the same result.
const arr = null; let result = []; if (Array.isArray(arr)) { result = arr.flatMap(str => str.split(' ')); } console.log(result); // ๐๏ธ []
If the value is an array, we call the flatMap()
method on it and set the
result
variable to the output.
flatMap()
If you have an array-like object, use the Array.from()
method to convert it to
an array before calling flatMap
.
const set = new Set(['one two', 'three four']); const result = Array.from(set).flatMap(str => str.split(' ')); console.log(result); // ๐๏ธ ['one', 'two', 'three', 'four']
We converted the value to an array before calling the flatMap
method.
You could also use the spread syntax (...) to achieve the same result.
const set = new Set(['one two', 'three four']); const result = [...set].flatMap(str => str.split(' ')); console.log(result); // ๐๏ธ ['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.
If you have an object that has an array property, access the relevant property
before calling flatMap()
.
const obj = { example: ['one two', 'three four'], }; const result = obj.example.flatMap(str => str.split(' ')); console.log(result); // ๐๏ธ [ 'one', 'two', 'three', 'four' ]
We accessed a property on the object that points to an array before calling the
Array.flatMap()
method.
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.
Ensure you have parsed the value to a native JavaScript array before calling the `flatMap`` method.