rashmi agar
30 posts
Mar 08, 2025
10:35 PM
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javascript flatmap method is a powerful tool for working with arrays, combining mapping and flattening in a single step. It is particularly useful when you want to transform an array and remove nesting in one go.
What is flatMap()?
The flatMap() method first maps each element using a mapping function and then flattens the result by one level. It is essentially a shortcut for calling .map() followed by .flat(1).
Syntax:
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const newArray = array.flatMap(callback(element, index, array), thisArg);
callback: A function to execute on each element of the array.
thisArg (optional): Value to use as this inside the callback function.
Example Usage:
1. Flattening an array of arrays:
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const arr = [[1], [2], [3]];
const result = arr.flatMap(x => x);
console.log(result); // Output: [1, 2, 3]
2. Transforming and flattening in one step:
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const words = ["hello", "world"];
const result = words.flatMap(word => word.split(""));
console.log(result); // Output: ['h', 'e', 'l', 'l', 'o', 'w', 'o', 'r', 'l', 'd']
When to Use flatMap()?
When mapping and flattening are both needed.
When dealing with nested arrays that need to be processed and reduced to a simpler form.
When improving performance over .map().flat(1).
Caveats:
flatMap() only flattens one level. If you need deeper flattening, you still need to use .flat(Infinity).
It does not modify the original array but returns a new one.
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