blocks|key|382516|text|问题中发布的代码无法生成该错误，因为Project不是用户定义的函数/有效的构造函数。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|382517|function+x(a,b,c){}
new+x(1,2,3);+++++++++++++++//+produces+no+errors|code-block|syntax|javascript|382518|你可能做过这样的事情：|382519|function+Project(a,b,c)+{}
Project+=+{};+++++++++++++++//+or+possibly+++Project+=+new+Project
new+Project(1,2,3);+++++++++//+->+TypeError:+Project+is+not+a+constructor|382520|使用var的变量声明是hoisted，因此总是在代码的其余部分之前进行计算。因此，这也可能导致问题：|382521|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
}|382522|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/JavaScript_syntax#hoisting^0|I|7|0|0|0|0|2|3|B|7|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|16|8|@$9|17|A|18|B|C]]|D|@$9|19|A|1A|1|1B]]|E|$]]|$1|Q|3|R|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

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

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

You've probably done something like this:

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

Variable declarations using <code>var</code> are <a href="https://en.wikipedia.org/wiki/JavaScript_syntax#hoisting" rel="noreferrer">hoisted</a> and thus always evaluated before the rest of the code. So, this can also be causing issues:

<pre><code>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
}
</code></pre>

blocks|key|598484|text|我也用谷歌搜索了一下，找到了这个解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|598485|你在某个地方有一个不是函数的变量Project。那么new操作员就会对此抱怨。在您应该将其用作构造器的地方尝试console.log(Project)，您会找到它。|offset|length|style|CODE|598486|entityMap^0|0|G|7|Q|3|1J|K|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]|$D|N|E|O|F|G]|$D|P|E|Q|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|I|$]]

I've googled around also and found this solution:

You have a variable <code>Project</code> somewhere that is not a function. Then the <code>new</code> operator will complain about it. Try <code>console.log(Project)</code> at the place where you would have used it as a construcotr, and you will find it.

blocks|key|598538|text|在我的例子中，我使用了原型名称作为对象名称。例如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|598539|function+proto1()
{}

var+proto1+=+new+proto1();|code-block|syntax|javascript|598540|这是一个愚蠢的错误，但可能会对我这样的人有所帮助;)|598541|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

In my case I was using the prototype name as the object name. For e.g.

<pre><code>function proto1()
{}

var proto1 = new proto1();
</code></pre>

It was a silly mistake but might be of help to someone like me ;)

blocks|key|382685|text|对于我的项目，问题原来是由require()调用创建的循环引用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382686|y.js:
var+x+=+require("./x.js");
var+y+=+function()+{+console.log("result+is+"+%2B+x();+}
module.exports+=+y;

x.js:
var+y+=+require("./y.js");
var+my_y+=+new+y();+//+<-+TypeError:+y+is+not+a+constructor
var+x+=+function()+{+console.log("result+is+"+%2B+my_y;+}
module.exports+=+x;|code-block|syntax|javascript|382687|原因是，当它试图初始化y时，它会创建一个临时的"y“对象(不是class，而是object!)在依赖系统中，不知何故它还不是一个构造函数。然后，当x.js完成定义后，它可以继续使y成为构造函数。只是，x.js在尝试使用非构造函数y时会出现错误。|382688|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

For my project, the problem turned out to be a circular reference created by the require() calls:

<pre><code>y.js:
var x = require("./x.js");
var y = function() { console.log("result is " + x(); }
module.exports = y;

x.js:
var y = require("./y.js");
var my_y = new y(); // &lt;- TypeError: y is not a constructor
var x = function() { console.log("result is " + my_y; }
module.exports = x;
</code></pre>

The reason is that when it is attempting to initialize y, it creates a temporary "y" object (not class, object!) in the dependency system that is somehow not yet a constructor. Then, when x.js is finished being defined, it can continue making y a constructor. Only, x.js has an error in it where it tries to use the non-constructor y.

blocks|key|382732|text|在我的例子中，我忘记了函数定义末尾的打开和关闭括号，将我的所有代码包装在导出的模块中。也就是说，我有：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382733|(function+()+{
++'use+strict';

++module.exports.MyClass+=+class{
++...
);|code-block|syntax|javascript|382734|而不是：|382735|(function+()+{
++'use+strict';

++module.exports.MyClass+=+class{
++...
)();|382736|编译器不会报错，但是导入模块中的require语句没有设置被赋值的变量，所以在您尝试构造它的时候它是未定义的，并且它会给出TypeError:+MyClass+is+not+a+constructor错误。|offset|length|style|CODE|382737|entityMap^0|0|0|0|0|1P|13|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

In my case I'd forgotten the open and close parantheses at the end of the definition of the function wrapping all of my code in the exported module. I.e. I had:

<pre><code>(function () {
 'use strict';

 module.exports.MyClass = class{
 ...
);
</code></pre>

Instead of:

<pre><code>(function () {
 'use strict';

 module.exports.MyClass = class{
 ...
)();
</code></pre>

The compiler doesn't complain, but the require statement in the importing module doesn't set the variable it's being assigned to, so it's undefined at the point you try to construct it and it will give the <code>TypeError: MyClass is not a constructor</code> error.

blocks|key|382781|text|为了补充@wprl的答案，ES6对象方法速记，就像箭头函数一样，也不能用作构造函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382782|const+o+=+{
++a:+()+=>+{},
++b()+{},
++c:+function+()+{}
};

const+{+a,+b,+c+}+=+o;

new+a();+//+throws+"a+is+not+a+constructor"
new+b();+//+throws+"b+is+not+a+constructor"
new+c();+//+works|code-block|syntax|javascript|382783|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

To add to @wprl's answer, the ES6 object method shorthand, like the arrow functions, cannot be used as a constructor either. 

<pre><code>const o = {
 a: () =&gt; {},
 b() {},
 c: function () {}
};

const { a, b, c } = o;

new a(); // throws "a is not a constructor"
new b(); // throws "b is not a constructor"
new c(); // works
</code></pre>

blocks|key|382818|text|我有一个类似的错误，我的问题是变量名和构造函数名的名称和大小写是相同的，这是不起作用的，因为javascript将目标构造函数解释为新创建的变量。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382819|换句话说：|382820|function+project(name){
++++this.name+=+name;
}

//elsewhere...

//this+is+no+good!+name/case+are+identical+so+javascript+barfs.+
let+project+=+new+project('My+Project');|code-block|syntax|javascript|382821|不过，只需更改大小写或变量名即可解决此问题：|382822|//with+a+capital+'P'
function+Project(name){
++++this.name+=+name;
}

//elsewhere...

//works!+class+name/case+is+dissimilar+to+variable+name
let+project+=+new+Project('My+Project');|382823|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I had a similar error and my problem was that the name and case of the variable name and constructor name were identical, which doesn't work since javascript interprets the intended constructor as the newly created variable.

In other words:

<pre><code>function project(name){
 this.name = name;
}

//elsewhere...

//this is no good! name/case are identical so javascript barfs. 
let project = new project('My Project');
</code></pre>

Simply changing case or variable name fixes the problem, though:

<pre><code>//with a capital 'P'
function Project(name){
 this.name = name;
}

//elsewhere...

//works! class name/case is dissimilar to variable name
let project = new Project('My Project');
</code></pre>

blocks|key|382838|text|这是因为您必须在代码中使用另一个名为"project“的变量。像var+project+=+{}这样的东西|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|382839|要使代码正常工作，请按如下方式进行更改：|382840|进入var+project1+=+{}的var+project+=+{}|382841|entityMap^0|W|G|0|0|2|H|K|G|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|K|$]]

It is happening because you must have used another variable named "project" in your code. Something like 
<code>var project = {}</code>

For you to make the code work, change as follows:

<code>var project = {}</code> into <code>var project1 = {}</code>

blocks|key|382863|text|Car.js|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382864|class+Car+{
+getName()+{return+'car'};
}
export+default+Car;|code-block|syntax|javascript|382865|TestFile.js|382866|const+object+=+require('./Car.js');
const+instance+=+new+object();|382867|错误:+TypeError:实例不是构造函数|382868|打印对象的内容|382869|object+=+{default:+Car}|382870|将default附加到require函数，它将作为构造器工作|382871|const+object+=+require('object-fit-images').default;
const+instance+=+new+object();
instance.getName();|382872|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|14|8|@]|9|@]|A|$E|F]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

Car.js

<pre><code>class Car {
 getName() {return 'car'};
}
export default Car;
</code></pre>

TestFile.js

<pre><code>const object = require('./Car.js');
const instance = new object();
</code></pre>

error: TypeError: instance is not a constructor

printing content of object

<pre><code>object = {default: Car}
</code></pre>

append default to the require function and it will work as contructor

<pre><code>const object = require('object-fit-images').default;
const instance = new object();
instance.getName();
</code></pre>

blocks|key|598768|text|我只想补充一点，如果构造函数是从不同的文件中调用的，那么像忘记使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|598769|module.exports+=+NAME_OF_CONSTRUCTOR|code-block|syntax|javascript|598770|还会导致“不是构造函数”异常。|598771|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I just want to add that if the constructor is called from a different file, then something as simple as forgetting to export the constructor with

<pre><code>module.exports = NAME_OF_CONSTRUCTOR
</code></pre>

will also cause the "Not a constructor" exception.

blocks|key|598801|text|我在一个文件中有一个类，我要将其导入到测试文件中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|598802|//Vec.js
class+Vec+{

}

module.exports.Vec+=+Vec;|code-block|syntax|javascript|598803|改变|598804|//Vec.test.js
const+Vec+=+require('./Vec');
const+myVec+=+new+Vec();+//TypeError:+Vec+is+not+a+constructor|598805|至|598806|//Vec.test.js
const+{Vec}+=+require('./Vec');
const+myVec+=+new+Vec();+//Succeeds!|598807|为我解决了这个错误。|598808|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

I have a class in one file that I'm importing into a test file:

<pre class="lang-js prettyprint-override"><code>//Vec.js
class Vec {

}

module.exports.Vec = Vec;
</code></pre>

Changing 

<pre class="lang-js prettyprint-override"><code>//Vec.test.js
const Vec = require('./Vec');
const myVec = new Vec(); //TypeError: Vec is not a constructor
</code></pre>

to 

<pre class="lang-js prettyprint-override"><code>//Vec.test.js
const {Vec} = require('./Vec');
const myVec = new Vec(); //Succeeds!
</code></pre>

resolved this error for me.

blocks|key|382908|text|为了将我发现的解决方案添加到这个问题中，我从另一个文件中包含了一个类，而我试图在其中实例化它的文件给出了“不是构造函数”错误。最终，问题是在定义类之前，另一个文件中有几个未使用的需求。我不知道他们为什么会弄坏它，但移除它们就能修复它。一定要检查你正在思考的步骤之间是否隐藏着什么。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382909|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

To add the solution I found to this problem when I had it, I was including a class from another file and the file I tried to instantiate it in gave the &quot;not a constructor&quot; error. Ultimately the issue was a couple unused requires in the other file before the class was defined. I'm not sure why they broke it, but removing them fixed it. Always be sure to check if something might be hiding in between the steps you're thinking about.

blocks|key|382939|text|当我尝试将BS5ModalJS与webpack结合使用时，我刚刚遇到了类似的错误，这意味着我正在尝试导入js文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|382940|因为提供的单个.js文件是为通过脚本标记使用而设计的，所以我花了一段时间才意识到，为了避免"BSModal不是构造函数“错误，我必须进入他们的代码并添加：|382941|export+{BSModal}|code-block|syntax|javascript|382942|然后我就可以使用|382943|import+{+BSModal+}+from+'./../thirdparty/BS5ModalJS/BS5Modal.js';|382944|并这样做|382945|让myModal+enter+code+here=新的BSModal(...)|offset|length|style|CODE|382946|而不会得到那个错误。|382947|因此，如果您使用的是webpack，可能要确保将类和函数导出(并因此可用)给调用者。|382948|entityMap^0|0|0|0|0|0|0|9|F|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|16|8|@$Q|17|R|18|S|T]]|9|@]|A|$]]|$1|U|3|V|5|6|7|19|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

I just had a similar error when trying to use the BS5ModalJS in conjunction with webpack, meaning I was trying to import the js file.
Because the single .js file provided was designed to be used via the script tags, it took a while for me to realise that to avoid the &quot;BSModal is not a constructor&quot; error, I had to go into their code and add:
<pre><code>export {BSModal}
</code></pre>
I was then able to use
<pre><code>import { BSModal } from './../thirdparty/BS5ModalJS/BS5Modal.js';
</code></pre>
and do
let myModal <code>enter code here</code>= new BSModal(...)
without getting that error.
So if you're using webpack, perhaps make sure the classes and functions are exported (and therefore available) to the callers.

blocks|key|383010|text|在browse+(假设您的应用程序正在运行)中，检查、编写源代码，并确保加载了构造函数的javascript文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|383011|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

In browse (assuming your app is running), inspect, source, and make sure the javascript file for the constructor is loaded.

I am defining an object like this:
<pre><code>function Project(Attributes, ProjectWidth, ProjectHeight) {
 this.ProjectHeight = ProjectHeight;
 this.ProjectWidth = ProjectWidth;
 this.ProjectScale = this.GetProjectScale();
 this.Attributes = Attributes;

 this.currentLayout = '';

 this.CreateLayoutArray = function()
 {....}
}
</code></pre>
I then try to create an instance like this:
<pre><code>var newProj = new Project(a,b,c);
</code></pre>
but this exception is thrown:
<pre><code>Project is not a constructor
</code></pre>
What could be wrong? I googled around a lot, but I still can't figure out what I am doing wrong.

Javascript "Not a Constructor" Exception while creating objects

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我像这样定义了一个对象：function Project(Attributes, ProjectWidth, ProjectHeight) {    this.ProjectHeight = ProjectHeight;    this.ProjectWidth = ProjectWidth;    this.Proj...

问创建对象时Javascript "Not a Constructor“异常
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问创建对象时Javascript "Not a Constructor“异常
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