cjahv/could-be-class

Checks if an object could be an instantiable class.

couldBeClass

Checks if an object could be an instantiable class.

This module also works with those classes that are written in ES5 style.

Example

"use strict";

const assert = require("assert");
const couldBeClass = require("could-be-class").default;

var str = "This is a string";
assert.ok(!couldBeClass(str));

var num = 123;
assert.ok(!couldBeClass(num));

class A { }
assert.ok(couldBeClass(A));

function B() {
    this.name = this.constructor.name;
}
assert.ok(couldBeClass(B));

function C() {
    this["name"] = this.constructor.name;
}
assert.ok(couldBeClass(C));

function D() { }
D.prototype.show = function () { }
assert.ok(couldBeClass(D));

function E() { }
Object.defineProperty(E.prototype, "size", {
    get() {
        return this.length;
    }
});
assert.ok(couldBeClass(E));

function TsEs5Class() {
    var _this = _super.call(this) || this;
    _this.desc = "This class form might be generated from TypeScript to ES5";
}
assert.ok(couldBeClass(TsEs5Class));

function notClass() {
    console.log("this is not a class");
}
assert.ok(!couldBeClass(notClass));

function aMethod() {
    this.desc = "this is a method instead of a class";
}
assert.ok(!couldBeClass(aMethod));

function default_1() {
    this.dec = "this might be a class generated by typescript";
}
assert.ok(couldBeClass(default_1));

function default_2() {
    console.log("this is not class");
}
assert.ok(!couldBeClass(default_2));

function* GenFunc() {
    this.desc = "Error will be thrown if trying to instantiate a Generator function.";
}
assert.ok(!couldBeClass(GenFunc));

if (parseFloat(process.version.slice(1)) >= 7.6) {
    // this block should only appear when you NodeJS version higher than 7.6, 
    // otherwise a SyntaxError will be thrown.
    async function AsyncFunc() {
        this.desc = "Error will be thrown if trying to instantiate an async function.";
    }
    assert.ok(!couldBeClass(AsyncFunc));
}

console.log("#### OK ####"); // should outout OK

Tip

Commonly, any functions (except async, generator and arrow functions) in JavaScript could be instantiated as a class constructor, however, in most cases, a class written in ES5 style will carry some special fingerprints that the detector can test if it could be a class constructor or just a pure function.

WARN This module only performs about 98% percent of accuracy when testing ES5 class.