无法使用Sinon在类中存根箭头函数

Question

• Sinon version : v2.0.0-pre.2
• Environment : Windows 10
• Other libraries you are using: Typescript, babel, mocha, chai

What did you expect to happen?

I expected to be able to stub an arrow function in a class.

What actually happens

I can't stub an arrow function, however, I can stub the class prototype function.

FAILED TESTS:
  ExampleClass tests
    × should stub thisDoesntWork arrow function
      Chrome 52.0.2743 (Windows 10 0.0.0)
    TypeError: Attempted to wrap undefined property thisDoesntWork as function
        at wrapMethod (webpack:///~/sinon/pkg/sinon.js:3138:0 <- test-bundler.js:7377:21)
        at Object.stub (webpack:///~/sinon/pkg/sinon.js:2472:0 <- test-bundler.js:6711:12)
        at Context.<anonymous> (webpack:///src/stores/sinon.test.ts:22:51 <- test-bundler.js:96197:72)

How to reproduce

export class ExampleClass {
    thisWorks() {
        return 0;
    }

    thisDoesntWork = () => {
        return 0;
    }
}

describe("ExampleClass tests", () => {
    it("should stub thisWorks function", () => {
        let stubFunctionA = sinon.stub(ExampleClass.prototype, "thisWorks");
    });
    it("should stub thisDoesntWork arrow function", () => {
        let stubFunctionB = sinon.stub(ExampleClass, "thisDoesntWork");
    });
});

Answer 1

I've never used sinon , but in their documentation it states for the sinon.stub function that it:

Replaces object.method with a stub function

If you look at the compiled js code of your ExampleClass :

var ExampleClass = (function () {
    function ExampleClass() {
        this.thisDoesntWork = function () {
            return 0;
        };
    }
    ExampleClass.prototype.thisWorks = function () {
        return 0;
    };
    return ExampleClass;
}());

Then you'll see that ExampleClass.prototype.thisWorks is defined, but there's no ExampleClass.thisDoesntWork definition, not even ExampleClass.prototype.thisDoesntWork .

The thisDoesntWork method is added only in the constructor (arrow functions aren't really class methods, they are just class members with a function type).

I suspect that this will work:

describe("ExampleClass tests", () => {
    it("should stub thisDoesntWork arrow function", () => {
        let stubFunctionB = sinon.stub(new ExampleClass(), "thisDoesntWork");
    });
});