从 JavaScript 数组中获取接下来的两个元素

Question

I have a javascript array And i wish to get the next preceeding two elements using a function and slice. I'm not getting the result. Is there any way to go around this?

 var arr = [1,2,3,4,5,6,7,8,9]

 function get(arr){
    for(var i=0; i<arr.length; i++){
       console.log(arr.slice(i, 3))
    }}


// Now when I call the function

    get(arr)

// Funny output

[1, 2, 3]
[2, 3]
[3]
[]
[]
[]
[]
[]
[]
[]
[]

Answer 1

You need the index instead of the length with Array#slice

Syntax

arr.slice([begin[, end]])

...

end Optional

Zero-based index before which to end extraction. slice extracts up to but not including end.

For example, slice(1,4) extracts the second element through the fourth element (elements indexed 1, 2, and 3).

A negative index can be used, indicating an offset from the end of the sequence. slice(2,-1) extracts the third element through the second-to-last element in the sequence.

If end is omitted, slice extracts through the end of the sequence ( arr.length ).

If end is greater than the length of the sequence, slice extracts through to the end of the sequence ( arr.length ).

 function get(arr) { for (var i = 0; i < arr.length; i++) { console.log(arr.slice(i, i + 3)); } } var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9]; get(arr);

Answer 2

The second parameter to slice() is end index. So what you're saying is give me all elements from i to index 3 (not-inclusive).

What you should be saying is slice(i, i+3)

Answer 3

slice(i, 3) basically means you want a new array with elements between the index before index i and index 3 . You can just use a simple for loop instead to return the proceeding two elements of each element like this:

 var arr = [1,2,3,4,5,6,7,8,9] function get(x){ for (i = 0; i < x.length - 2; i++){ console.log("The proceeding two elements of " + x[i] + " is " + x[i+1] + " and " + x[i+2]); } } get(arr);

NB The - 2 in the for loop's x.length - 2 is to prevent returning an undefined result since the last two elements won't have two proceeding elements.

---

Or if you prefer using slice() , you can do this:

 var arr = [1,2,3,4,5,6,7,8,9] function get(x){ for (i = 0; i < x.length - 2; i++){ console.log(x.slice(i, i+3)); } } get(arr);

Again, the - 2 in the for loop's x.length - 2 is to prevent returning an undefined result or an incomplete result since the last two elements won't have two proceeding elements.