javascript - 用于打印二维数组的嵌套 for 循环。迭代是否未定义？

Question

我已经尝试了下面代码的许多变体，即在 while 中交换。我有一个动态创建和添加的数组。它创建了一个空的联赛表。当我遍历数组并打印出表格时，第一个循环总是返回未定义？我的控制台记录了所有内容，但无法找出原因。我认为这与内部循环变量有关，但我的想法已经用完了。有人可以解释为什么所有循环都会发生这种情况吗？我在这里阅读了一些问题，有些人谈到变量在第一个循环中被视为字符串，但我不明白。

league = [];

$('#butt').on('click',function(){
    var name = $('.input1').val();
    x = $('#demo');
    x.html(name);
    person(name,0,0,0,0,0);
});

function person(first,w,d,l,gf,ag) {
    this.Name = first;
    this.wins = w;
    this.draws = d;
    this.lose = l;
    this.goalsfor = gf;
    this.goalsag =ag;
    newTeam = new Array    

    (this.Name,this.wins,this.draws,this.lose,this.goalsfor,this.goalsag);


    league.push(newTeam);
    teamRow = league[0][0];
    makeLeague();
}

function makeLeague(){

    var tableStart = "<table>"
    var tableEnd = "</table>"
    var tableMid ;
    var secondtab = $('#demo1');

    leagueSize = league.length;

    console.log("league length is   " + league.length);

    for(k=0; k<league.length; k++){
        tableMid += "<tr>";
        for(i=0; i< 6; i++){
            tableMid += "<td> " + league[k][i] + "</td>";
        }
        tableMid += "</tr>";
    }

    secondtab.html(tableStart + tableMid + tableEnd);
}

Answer 1

当 person 应该用作构造函数时，您将其用作普通函数。尝试使用 new person(name, 0, 0, 0, 0, 0); 代替(并可能将其存储到变量中)。

另外，作为John Sheridan mentions ，您还需要初始化 tableMid 变量，然后才能附加到它，如下所示:var tableMid = "";。

这是代码的清理版本。请注意您应该包含的 var 声明以避免范围问题。

var league = [];

$('#butt').on('click', function() {
    var name = $('.input1').val();
    var x = $('#demo');
    x.html(name);
    var person = new Person(name, 0, 0, 0, 0, 0);
});

function Person(first, w, d, l, gf, ag) {
    this.Name = first;
    this.wins = w;
    this.draws = d;
    this.lose = l;
    this.goalsfor = gf;
    this.goalsag = ag;
    var newTeam = [this.Name, this.wins, this.draws, this.lose, this.goalsfor, this.goalsag];

    league.push(newTeam);
    var teamRow = league[0][0];
    makeLeague();
}

function makeLeague() {
    var tableStart = "<table>";
    var tableEnd = "</table>";
    var tableMid = "";
    var secondtab = $('#demo1');

    for (var k = 0; k < league.length; k++) {
        var team = league[k];
        tableMid += "<tr>";
        for (var i = 0; i < team.length; i++) {
            tableMid += "<td> " + team[i] + "</td>";
        }
        tableMid += "</tr>";
    }

    secondtab.html(tableStart + tableMid + tableEnd);
}