javascript - 在两个方向上迭代一个范围

Question

在两个方向上通过某个范围进行循环迭代是一项非常常见且简单的任务：

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));

上面的代码完美运行，但我花了大约一个小时试图摆脱双重if检查。

如果没有if有什么办法解决吗？可能是单线？

标签： javascriptarraysshorthand

Answer 1

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

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));