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Use the initialValue argument of reduce
Array.reduce's second argument is an optional initial value. Based on whether it's supplied or not, there are three cases:
- If
initialValueis set, it will be the firstaccumulator - If
initialValueis not set, the first element will be the firstaccumulator - If
initialValueis not set and the array is empty, an error is raised
The initialValue is usually considered the "zero element" of the operation defined in the callback. A few examples:
- For addition, it's
0 - For multiplication, it's
1 - For array concatenation, it's
[]
But not all operations have a zero element.
This code throws an error if the array is empty:
array.reduce((acc, e) => acc + e);
Avoid this error case by defining an initial value, if there is an applicable one. The following code returns 0 for the empty array:
array.reduce((acc, e) => acc + e, 0);