JavaScript uses Array filter() to compress sparse arrays

What is a sparse array

The indexes of array elements do not have to be consecutive, there can be gaps between them. Every javaScript array has a length property. For non-sparse arrays, this property is the number of array elements; for sparse arrays, length is greater than the number of all elements.

The Array filter() method skips missing elements in a sparse array, and its return array is always dense. This article introduces you to the relevant knowledge of using the Array filter() method to compress sparse arrays in JavaScript. Friends who need it can refer to it. I hope it can help you.

(1) Compress the vacancies of the sparse array:

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

(2) Compress the vacancies of the sparse array, and delete undefined and null elements:

var dense = sparse.filter( function(currentValue) 
{ 
return currentValue !== undefined && currentValue!= null;
} 
)

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