Javascript：对嵌套 for 循环的工作方式感到困惑答案

【问题标题】：Javascript: confused about how nested for loops workJavascript：对嵌套 for 循环的工作方式感到困惑
【发布时间】：2011-09-08 10:10:37
【问题描述】：

为什么嵌套的for loops 的工作方式与以下示例中的一样：

var times = [
            ["04/11/10", "86kg"], 
            ["05/12/11", "90kg"],
            ["06/12/11", "89kg"]
];

for (var i = 0; i < times.length; i++) {
        var newTimes = [];
        for(var x = 0; x < times[i].length; x++) {
            newTimes.push(times[i][x]);
            console.log(newTimes);  


        }

    }

在这个例子中，我认为 console.log 会给我以下输出：

["04/11/10"]
["86kg"]
["05/12/11"]
["90kg"]
["06/12/11"]
["89kg"]

但是，我实际上得到了这个：

["04/11/10"]
["04/11/10", "86kg"]
["05/12/11"]
["05/12/11", "90kg"]
["06/12/11"]
["06/12/11", "89kg"]

有人能帮我理解这个吗？

编辑：

感谢您的所有回复！

【问题讨论】：

标签： javascript arrays for-loop

【解决方案1】：

// remember that the increment of the counter variable
// is always executed after each run of a loop


for (var i = 0; i < n; i++) {
    // some statement(s) to do something.. 

        // initializes child-loop counter in the first run of the parent-loop
        // resets child-loop counter in all following runs of the parent-loop
        // while i is greater than 0 and lower than n

    for (var j = 0; j < p; j++) {
        // some statement(s) to do something..

            // initializes grandchild-loop counter in the first run of the child-loop
            // resets grandchild-loop counter in all following runs of the child-loop
            // while j is greater than 0 and lower than p

        for (var k = 0; k < q; k++) {
            // some statement(s) to do something..
            // or add more internal loop-nestings if you like..
        }
    }
}

// if the counter variables of the descendent-loops were set before the loop-nesting,
// the inner loops would only run once, because the counter would keep the value
// of the abortion condition after the loop is finished

【讨论】：

【解决方案2】：

问题在于内部循环的第二轮，它将第二个元素推入 newTimes。无论如何我不明白内循环的原因。你可以写得更简单：

var times = [
            ["04/11/10", "86kg"], 
            ["05/12/11", "90kg"],
            ["06/12/11", "89kg"]
];

for (var i = 0; i < times.length; i++) {
    console.log(time[i][0]);  
    console.log(time[i][1]);   
}

【讨论】：

【解决方案3】：

如果日志语句会读取，您的输出将是合适的

console.log(times[i][x]);

相反，您输出完整的新列表 newTimes，该列表在内部循环外部初始化并随着每次内部循环迭代而增长。

【讨论】：

【解决方案4】：

这样做：

var newTimes = [];
for (var i = 0; i < times.length; i++) {
        for(var x = 0; x < times[i].length; x++) {
            newTimes.push(times[i][x]);
            console.log(newTimes);  


        }

    }

每次循环都在重新初始化 newTimes。

【讨论】：

【解决方案5】：

您在每个循环上重新定义newTimes，并且在每次列推送时输出到控制台。

var times = [
            ["04/11/10", "86kg"], 
            ["05/12/11", "90kg"],
            ["06/12/11", "89kg"]
];
 var newTimes = [];
for (var i = 0; i < times.length; i++) {     
        for(var x = 0; x < times[i].length; x++) {
            newTimes.push(times[i][x]);
        }
    }
    console.log(newTimes);

返回：["04/11/10", "86kg", "05/12/11", "90kg", "06/12/11", "89kg"] http://jsfiddle.net/niklasvh/SuEdt/

【讨论】：