如何在Nodejs调试控制台视图中更改对象的字符串表示形式 [英] How to change string representation of objects in Nodejs debug console view

问题描述

如何在nodejs调试控制台中更改对象实例的字符串表示形式。是否有一种方法（如.NET中的 toString（））我可以覆盖？

请考虑以下代码：

  class SomeObject {
 constructor（）{
 this._varA =some text; 
 this._varB = 12345; 
 this._varC =更多文字; 
 this._varD = true; 
 this._varE = 0.45; 
} 
 
 toString（）{
返回我的对象的自定义文本表示; 
} 
} 
 
 var array = []; 
 
 array.push（new SomeObject（））; 
 array.push（new SomeObject（））; 
 array.push（new SomeObject（））; 
 
 console.log（array）; 
  

这会产生以下结果：

但是在我使用的其他环境和编程语言中，覆盖 toString（）方法会显示结果 toString（）（在上面的示例我的对象的自定义文本表示）而不是创建的动态文本表示通过调试器（在上面的示例代码中： SomeObject {_varA：some text，_ varB：12345，_varC：some some text，...} ） - 我不怀疑一分钟，当没有定义自定义替代品时，它非常有用。

我也意识到 console.log（ array.toString（））; 甚至 console.log（array.map（t => t.toString（）））; 将产生类似于我所追求的东西，然而这是预先的让我通过调试导航浏览对象，即。钻进对象图。

如果不可能，其他人会从中受益吗？如果有足够的兴趣，我可以考虑定义并实现它作为一个功能。

解决方案

当你做 console.log 它在 util.js 内部调用 formatValue ，它有一个下面检查

  const maybeCustomInspect = value [customInspectSymbol] || value.inspect; 
  

这意味着如果您的值有 inspect 它被调用的方法然后你可以返回 toString 。因此，将代码更改为

  class SomeObject {
 constructor（）{
 this._varA =some文本; 
 this._varB = 12345; 
 this._varC =更多文字; 
 this._varD = true; 
 this._varE = 0.45; 
} 
 
 inspect（depth，opts）{
 return this.toString（）; 
} 
 
 toString（）{
返回我的对象的自定义文本表示; 
} 
} 
 
 var array = []; 
 
 array.push（new SomeObject（））; 
 array.push（new SomeObject（））; 
 array.push（new SomeObject（））; 
 
 console.log（array）; 
  

打印

  [我的对象的自定义文本代表，
我的对象的自定义文本代表，
我的对象的自定义文本代表] 
  

Nodejs也有相同的文件

信息是由调试器重建的，为您提供有意义的表示。

现在 v8 debug api不知道我们想要代表它的差异就像我们为 console.log 所做的那样。现在可能在 V8 代码中有类似的东西类似，但查看源代码，我无法弄清楚是否存在这样的事情。所以你可能需要向拥有V8调试器api知识的人确认，如果存在这种类型的东西

如果不是你需要在IDE级别构建一些东西，再做一件事并不容易

How do I change the string representation of an object instance in nodejs debug console. Is there a method (like toString() in .NET) I can override?

Consider the following code:

class SomeObject{
    constructor(){
        this._varA = "some text";
        this._varB = 12345;
        this._varC = "some more text";
        this._varD = true;
        this._varE = 0.45;
    }

    toString(){
        return "custom textual rapresentation of my object";
    }
}

var array = [];

array.push(new SomeObject());
array.push(new SomeObject());
array.push(new SomeObject());

console.log(array);

This produces the following:

However in other environments and programming languages I have worked on, overriding the toString() method would show the result of toString() (in the example above "custom textual representation of my object") instead of the dynamic textual representation created by the debugger (in the example code above this is: SomeObject {_varA: "some text", _varB: 12345, _varC: "some more text", …}) - which I don't doubt for one minute it is very useful when a custom alternative is not defined.

I also realise that console.log(array.toString()); or even console.log(array.map(t=>t.toString())); will produce something similar to what I am after, however this then prevents me to navigate through the objects using the debug navigation ie. drill into the object graph.

If this is not possible, would others benefit from this? If there is enough interest, I can look into defining and implementing it as a feature.

解决方案

When you do console.log it internally calls formatValue in util.js, which has a below check

const maybeCustomInspect = value[customInspectSymbol] || value.inspect;

Which means if your value has a inspect method it gets called and then you can return the toString in the same. So change your code to

class SomeObject{
    constructor(){
        this._varA = "some text";
        this._varB = 12345;
        this._varC = "some more text";
        this._varD = true;
        this._varE = 0.45;
    }

    inspect(depth, opts) {
        return this.toString();
    }

    toString(){
        return "custom textual rapresentation of my object";
    }
}

var array = [];

array.push(new SomeObject());
array.push(new SomeObject());
array.push(new SomeObject());

console.log(array);

Makes it print

[ custom textual rapresentation of my object,
  custom textual rapresentation of my object,
  custom textual rapresentation of my object ]

Nodejs has documentation on the same too

https://nodejs.org/dist/latest-v8.x/docs/api/util.html#util_custom_inspection_functions_on_objects

The inspect method I used is deprecated as per documentation and the correct way to do it is below

const util = require('util');

class SomeObject{
    constructor(){
        this._varA = "some text";
        this._varB = 12345;
        this._varC = "some more text";
        this._varD = true;
        this._varE = 0.45;
    }

    [util.inspect.custom](depth, options) {
        return this.toString();
    }

    toString(){
        return "custom textual rapresentation of my object";
    }
}

var array = [];

array.push(new SomeObject());
array.push(new SomeObject());
array.push(new SomeObject());

console.log(array);

Edit: 28th-Mar-2018

So I launched the script using below

$ node --inspect-brk=54223 test.js 
Debugger listening on ws://127.0.0.1:54223/81094440-716b-42a5-895e-4ea2008e0dff
For help see https://nodejs.org/en/docs/inspector

And then ran a socat forwarder using below

$ socat -v TCP-LISTEN:54222,fork TCP:127.0.0.1:54223

When you debug the variable array in debugger, you get below output on the socat terminal

The information is that reconstructed by debugger to give you a meaningful representation.

Now the v8 debug api has no idea that we want to represent it differently, like we did for console.log. Now there may be something similar in V8 code that does something similar, but looking at the source code, I was not able to figure out there exists such a thing. So you may need to confirm from someone who has V8 debugger api knowledge, if something of this sort exists

If not the you need to construct something at the IDE level, which again is not a a easy thing to do

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