Javascript“Not a Constructor”创建对象时发生异常 [英] Javascript "Not a Constructor" Exception while creating objects

问题描述

我定义一个这样的对象：

I am defining an object like this:

function Project(Attributes, ProjectWidth, ProjectHeight)
{
    this.ProjectHeight = ProjectHeight;
    this.ProjectWidth = ProjectWidth;
    this.ProjectScale = this.GetProjectScale();
    this.Attributes = Attributes;

    this.currentLayout = '';

    this.CreateLayoutArray = function()
    {....}
}

然后我尝试创建和像这样的实例：

I then try to create and instance like this:

var newProj = new Project(a,b,c);

但是引发了这个execption：

But this execption is thrown:

Project is not a constructor

可能出错？

推荐答案

代码发布在问题不能产生该错误，因为 Project 不是用户定义的函数/有效的构造函数。

The code as posted in the question cannot generate that error, because Project is not a user-defined function / valid constructor.

function x(a,b,c){}
new x(1,2,3);               // produces no errors

你可能做了这样的事情：

You've probably done something like this:

function Project(a,b,c) {}
Project = {};               // or possibly   Project = new Project
new Project(1,2,3);         // -> TypeError: Project is not a constructor

变量声明总是在代码的其余部分之前进行求值。所以，这也可能是导致问题：

Variable declarations are always evaluated before the rest of the code. So, this can also be causing issues:

function Project(){}
function localTest() {
    new Project(1,2,3); // `Project` points to the local variable,
                        // not the global constructor!

   //...some noise, causing you to forget that the `Project` constructor was used
    var Project = 1;    // Evaluated first
}

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