在两个方向上迭代一个范围

Question

有一个非常常见和简单的任务，即在两个方向上通过某个范围进行循环迭代：

var currentIndex = 0;
var range = ['a', 'b', 'c', 'd', 'e', 'f'];

function getNextItem(direction) {
    currentIndex += direction;
    if (currentIndex >= range.length) { currentIndex = 0; }
    if (currentIndex < 0) { currentIndex = range.length-1; }

    return range[currentIndex];
}        
// get next "right" item
console.log(getNextItem(1));

// get next "left" item
console.log(getNextItem(-1));

上面的代码工作得很好，但我花了大约一个小时试图摆脱双重 if 检查。

如果没有if，有什么办法可以解决吗？也许是单线的？

Answer 1

要将两个 if 变成一个无条件语句，您可以将 range.length 添加到 currentIndex，然后使用模数：

var currentIndex = 0;
var range = ['a','b','c','d','e','f'];

function getNextItem(direction) {
    currentIndex = (currentIndex + direction + range.length) % range.length;
    return range[currentIndex];
}

// get next "right" item
console.log(getNextItem(1));
console.log(getNextItem(1));

// get next "left" item
console.log(getNextItem(-1));
console.log(getNextItem(-1));
console.log(getNextItem(-1));

console.log(getNextItem(4));
console.log(getNextItem(1));
console.log(getNextItem(1));
console.log(getNextItem(1));

在两个方向上迭代一个范围

Iterating through a range in both directions

javascript

arrays

shorthand