Javascript 和关联数组

Question

我是 JS 的新手，所以我尝试使用关联数组，但在我运行以下 JS 代码时出现错误。

Uncaught TypeError: Cannot set properties of undefined (setting 'x')

任何帮助都很棒。

var activeField;

fields = []; //  holds all the defined fields

function Field() {
  this.polypoints = [{}];
}

var field = new Field();
var Points;

fields.push(field);

activeField = (fields.length) - 1;
Points = fields[activeField].polypoints.length;
Points = Points + 1;
fields[activeField].polypoints[Points].x = 1;
fields[activeField].polypoints[Points].y = 1;

console.log("values in array:", activeField, polyPoints, fields);

Answer 1

当您创建 Points=Points+1; 时，Points 现在是 1。fields[activeField].polypoints[Points] 未定义 b/c 您还没有创建对象。该对象位于 fields[activeField].polypoints[0]。要添加对象，您必须创建。

fields[activeField].polypoints[Points]={x:1,y:1}

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