JavaScript：如何检测ES6类具有自己的构造函数？

Question

How to detect whether EcmaScript class has its own constructor? See code snippet below.

 class Person { constructor(name, age) { // <- Own constructor this._name = name; this._age = age; } } class Manager extends Person { // This class does not have it's own constructor } 

It seems there is no clear way to do this check.

Thank you all for time and help.

Answer 1

It's not bulletproof, but you could convert the constructor to a string, and see if it contains the word constructor( or something similar

 function hasOwnConstructor(instance) { var str = instance.constructor.toString(); return /class(.*?[^\\{])\\{([\\s\\n\\r\\t]+)?(constructor[\\s]+?\\()/.test(str); } class thing1 { method() { return this; } } class thing2 { constructor(argument) { return this; } } var ins1 = new thing1(); var ins2 = new thing2(); console.log( hasOwnConstructor(ins1) ); // false console.log( hasOwnConstructor(ins2) ); // true 

False positives could still be possible, but the regex makes the check quite strict, so it's not very plausable.

Answer 2

Inspect the constructor function.

class Example {

    constructor(prop1, prop2) {

    this.prop1 = prop1;
    this.prop2 = prop2;

      }
    }

You can pass parameters to your class via the constructor function that establishes properties which can be globally referenced when creating a new instance.

This line would pass int 1 and "test" as values to prop1 and prop2:

const exampleVar = new Example(1, "test");

and might render something like:

<Example prop1=1 prop2="test" />

Hope this helps. If it has a constructor function, there is a constructor, if it does not have the constructor function, then there is no constructor.