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.
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) ); // trueFalse positives could still be possible, but the regex makes the check quite strict, so it's not very plausable.
constructor( or something else, anything... Thats why this solution is not 100% safe.
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.
Personhas its own constructor and classManagerdon't.classandconstructoryou are NOT making classes and constructors Instead you are defining a function and maybe adding things to its prototype. I really don't see how this question (while interesting) has a relevant answer, because classes aren't real in JavaScript. Are you asking whether at run time you can see what the source code looked like? I think it is impossible without major hacks....