无休止地向后移动数组
[英]Endlessly moving through an array backwards
问题描述
I've got to be able moving through an array forwards and backwards.
我必须能够前后移动数组。 Endlessly and without getting an index out of bounds-exception.无休止地并且不会使索引越界异常。
For moving forward I've known an elegant way using the modulo-operator.为了继续前进，我知道使用模运算符的一种优雅方式。 For the backwards moving I've had to figure out something myself.对于向后移动，我不得不自己想办法。
Here's my solution:这是我的解决方案：
const inc = document.getElementById("inc"); const dec = document.getElementById("dec"); const arr = ["One", "Two", "Three", "Four", "Five", "Six"]; let i = 0; inc.addEventListener("click", () => { i = (i + 1) % arr.length; console.log(arr[i]); }); dec.addEventListener("click", () => { i = i - 1; if (i === -1) { i = arr.length - 1; } console.log(arr[i]); });
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <title>JS Bin</title> </head> <body> <button id="inc">Inc</button> <button id="dec">Dec</button> </body> </html>
It works.有用。 But is there a more elegant solution for moving backwards?但是有没有更优雅的后退解决方案？
So that one can get rid of this ugly if-check.这样就可以摆脱这个丑陋的 if-check。
2 个解决方案
解决方案1
6 2019-12-14 13:56:33
You can still use the modulus operator.您仍然可以使用模运算符。 To go backwards, it'd be要倒退，那就是
i = (i - 1 + array.length) % array.length;
When i is 0, the partial result will be (0 - 1 + array.length) , which is array.length - 1 .当i为 0 时，部分结果将为(0 - 1 + array.length) ，即array.length - 1 。
For any value greater than 0 but less than array.length , the modulus operator maps the value greater than array.length to the correct index in range.对于任何大于 0 但小于array.length的值，模数运算符将大于array.length的值映射到范围内的正确索引。
解决方案2
5 已采纳 2019-12-14 14:05:49
Yes, you could use a single formula for both forwards and backwards by creating a common function move and pass the step as parameter.是的，您可以通过创建一个通用函数move并将step作为参数传递给forwards和backwards使用单个公式。
i = (i + step + arr.length ) % arr.length;
let arr = ["One", "Two", "Three", "Four", "Five", "Six"] , i = 0 function move(step){ i = (i + step + arr.length ) % arr.length; console.log(arr[i]); }
<button id="inc" onclick="move(1)">Inc</button> <button id="dec" onclick="move(-1)">Dec</button>
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