The Array filter () method is used in JavaScript to compress sparse arrays.

The Array filter () method is used in JavaScript to compress sparse arrays.

What is a sparse array?

The index of array elements does not have to be continuous, and there may be gaps between them. Each javaScript array has a length attribute. For non-sparse arrays, this attribute is the number of array elements; for sparse arrays, length is larger than the number of all elements.

The Array filter () method skips the missing elements in the sparse Array, and its returned Array is always dense.

(1) compression of sparse array vacancies:

Var dense = sparse. filter (function (currentValue) {return true ;});

(2) compress the vacancy of the sparse array and delete the undefined and null elements:

Var dense = sparse. filter (function (currentValue) {return currentValue! = Undefined & currentValue! = Null ;})

Summary

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