Codewars with Notes

1.ES6 array traversal syntax sugar =

It was used in c#linq, so it's not very strange.

var range = array.apply (null, Array (x)). Map ((_, i) = = ++i);

A method for filling an empty array with apply is applied.

Apply applies to arrays as well: passing an array to a function that does not accept an array as a parameter, flattening a two-dimensional array (e.g.). The function parameter has an array.

> Math.max.apply (null, [1, 5])10

2. Use recursion to calculate the sum of squares:

function cal (x) {    return x==1?1: (Cal (x-1) +x*x);}
>cal (10)

When x is 1000, the stack overflow is prompted.

Then use tail recursion:

function cal (x, y   ) {return x==0?1: (Cal (x-1,x*x) +y);         } >cal (10,0)385

Codewars Backstage no error. However, after reading a number of articles (e.g.http://bbs.csdn.net/topics/390317532) found that the tail recursion still can not escape stackoverflow problem. Actually tested, the above two function cal (30000) will give an error.

3. Sparse arrays

[,,].every (function(x) {return x==22222})true

A sparse array skips "empty elements" as it traverses. I haven't thought of a way yet.

The array of JS is actually a key-value pair of strings and values. Just a special object.

Codewars with Notes