在JavaScript中循环读取数组值

Question

我在JavaScript中有一个已定义这些值的数组：

var myStringArray = ["1","2","3","4","5","6","7","8","9","10"];

当我第一次调用函数函数时，我需要得到这个：

1
2
3

再次打电话给我需要：

4
5
6

再次打电话：

7
8
9

再次打电话：

10
1
2

再次打电话：

3
4
5

等等。 你得到了重点，显示了数组中的3个值，如果我们在数组的末尾，请从头开始阅读......我有一个具有远程控制功能的应用程序，并且具有向下和向上键。 当用户按下向下按钮从数组中获取这些值时，如上例所示，如果用户按下向上按钮，则需要从示例返回...所以在循环中读取数组（最后，数组从头开始读取，但始终显示三个值）。

我尝试使用这个：

var myStringArray = ["1","2","3","4","5","6","7","8","9","10"];
var arrayLength = myStringArray.length;
for (var i = 0; i < arrayLength; i++) {
    if (i<(6)) {
       console.log(myStringArray[i]);
    }
}

但是下次我调用这段代码时，它会从数组的开头显示，而不是继续读取其他值...我需要第二个计数器吗？

Answer 1

如果你是操纵你的原始数组OK，你通过它循环，你可以splice和concat类似下面（或者，如果你需要坚持原有的数组，你可以使用数组的一个克隆）：

 var myStringArray = ["1","2","3","4","5","6","7","8","9","10"]; var loopByX = function(x){ var y = myStringArray.splice(0,x); myStringArray = myStringArray.concat(y); return y; } console.log(loopByX(3)); console.log(loopByX(3)); console.log(loopByX(3)); console.log(loopByX(3)); console.log(loopByX(3)); 

如果你想要双向（就是你所说的那个？），正如评论中所提到的那样，你可以按照下面的方式进行，然后让你能够向后或向前进行，并且可以灵活地进行任意操作。数：

 var myStringArray = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]; var loopByX = function(x) { var len = myStringArray.length; // Ensure x is always valid but you can add any behaviour here in that case yourself. As an example I return an empty array. if (Math.abs(x) > len) { return []; } var y = x > 0 ? myStringArray.splice(0, x) : myStringArray.splice(len + x, len); myStringArray = x > 0 ? myStringArray.concat(y) : y.concat(myStringArray); return y; } console.log(loopByX(20)); // invalid number console.log(loopByX(-20)); // invalid number console.log(loopByX(-3)); console.log(loopByX(-6)); console.log(loopByX(3)); console.log(loopByX(4)); 

Answer 2

你可以采用一个切三个元素的函数，如果不可能，它也需要数组所需的第一个值。

 function take3() { var temp = array.slice(index, index += 3) index %= array.length; console.log(temp.concat(temp.length < 3 ? array.slice(0, index) : []).join(' ')); } var array = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"], index = 0; 

 <button onclick="take3()">take 3</button> 

使用动态计数的映射。

 function take(length) { console.log(Array.from({ length }, _ => array[++index, index %= array.length])); } var array = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"], index = -1; 

 <button onclick="take(3)">take 3</button> 

Answer 3

你的变量i是for循环的本地变量for这意味着它每次循环启动时基本上都会重置。 因此，首先让你变i全球。

 var i=0; function employeeNames(){ var empList = ["1","2","3","4","5","6","7","8","9","10"]; var output = []; var j=0; while(j<3) { output.push(empList[i]) i=(i+1)%empList.length; j++; } return output; } console.log(employeeNames()); console.log(employeeNames()); console.log(employeeNames()); console.log(employeeNames()); console.log(employeeNames()); 

Answer 4

如果您希望以不可变的方式实现循环循环

function loopArray(arr, step=3) {
    let i = 0;
    return function inner() {
        for (let j = 0; j < step; j++) {
            console.log(arr[i]);
            i = (i + 1) % arr.length;
        }
    };
 }

const func = loopArray(["1","2","3","4","5","6","7","8","9","10"], 3);
func();
func();
func();
func();
func();

Answer 5

@Igor Petev ，JavaScript的闭包是一个很好的概念，可以用来解决你的问题。

请阅读JavaScript的闭包 - w3schools文章。 它非常好，非常好。

我已经使用闭包的概念来解决这个问题。 如果您不理解我的代码或与此问题相关的任何其他内容，请发表评论。

请看下面的代码。

var get3items = (function () {

    var index = 0;
    var myStringArray = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"];
    var len = myStringArray.length

    return function () {
       for(var count = 0; count < 3; count += 1)
       {
           console.log(myStringArray[index]);

           if(index == (len - 1))
           {
               index = 0;
           }
           else {
               index += 1;
           }
       }
    }
})();

get3items (); // First call

console.log()
get3items (); // Second call

console.log()
get3items (); // Third call

console.log()
get3items (); // Fourth call

console.log()
get3items (); // Fifth call

/*
 1
 2
 3

 4
 5
 6

 7
 8
 9

 10
 1
 2

 3
 4
 5
*/

Answer 6

具有发电机功能的奇特解决方案：

function* cycle(arr) {
    let i=0;
    while (true) {
        yield arr[i++];
        i %= arr.length;
    }
}
function* chunksOf(n, iterable) {
    let chunk = [];
    for (const x of iterable) {
        chunk.push(x)
        if (chunk.length >= n) {
            yield chunk;
            chunk = [];
        }
    }
    if (chunk.length > 0)
        yield chunk;
}
function toFunction(iterator) {
    return () => iterator.next().value;
}
var myStringArray = ["1","2","3","4","5","6","7","8","9","10"];

const f = toFunction(chunksOf(3, cycle(myStringArray)));
console.log(f());
console.log(f());
console.log(f());
// …

Answer 7

如何使用发电机：

function* get3() {
  var myStringArray = ["1","2","3","4","5","6","7","8","9","10"];
  var index = 0;
  while (true) {
    yield [0, 1, 2].map(i => myStringArray[(index + i) % myStringArray.length])
    index = (index + 3) % myStringArray.length;
  }
}

调用此函数会返回一个对象，您可以调用.next() ，以获取下一组3：

var getter = get3();
console.log(getter.next().value); // ["1","2","3"]
console.log(getter.next().value); // ["4","5","6"]
console.log(getter.next().value); // ["7","8","9"]
// etc.

Answer 8

function* employeeNames(){
    var empList =  ["1","2","3","4","5","6","7","8","9","10"];

    for(var i =0; i<=empList.length; i++){
        yield empList[i];
    }
}

var emp;
emp = employeeNames();

它使用发电机功能......