双向迭代范围

Question

在两个方向上都有一定范围内的循环迭代是一个非常普遍且容易的任务：

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));

上面的代码运行完美，但是我花了大约一个小时试图摆脱双重if检查。

是否有任何方法可以解决是否没有问题？有点单线？

Answer 1

要将两个if转换为一个无条件语句，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));

Answer 2

CurrentIndex = CurrentIndex <1？range.length：（currentIndex> range.length？1）;

来源：Ternary Operators Java