Category: JavaScript Answers

Sometimes, we want to check multiple arguments on multiple calls for Jest spies with JavaScript.

In this article, we’ll look at how to check multiple arguments on multiple calls for Jest spies with JavaScript.

How to check multiple arguments on multiple calls for Jest spies with JavaScript?

To check multiple arguments on multiple calls for Jest spies with JavaScript, we can use the mockFn.mock.calls property.

For instance, we write

expect(mockFn.mock.calls).toEqual([
  [arg1, arg2],
  [arg1, arg2],
]);

to call expect with mockFn.mock.calls to get the arguments that mockFn is called with.

Then we call toEqual with a nested array that has the array of arguments for each call of mockFn to check if they match what we expect.

Conclusion

To check multiple arguments on multiple calls for Jest spies with JavaScript, we can use the mockFn.mock.calls property.

Sometimes, we want to write asynchronous functions for Node.js.

In this article, we’ll look at how to write asynchronous functions for Node.js.

How to write asynchronous functions for Node.js?

To write asynchronous functions for Node.js, we can use promises.

For instance, we write

const ace = async () => {
  const r = await new Promise((resolve, reject) => {
    resolve(true);
  });

  console.log(r);
};

to create the ace async function that invokes a promise.

We create the promise with the Promise constructor called with a callback that calls resolve with the resolve value of the promise.

We get the promise’s resolve value with await.

Conclusion

To write asynchronous functions for Node.js, we can use promises.

Sometimes, we want to call getElementById based on a partial string with JavaScript.

In this article, we’ll look at how to call getElementById based on a partial string with JavaScript.

How to call getElementById based on a partial string with JavaScript?

To call getElementById based on a partial string with JavaScript, we call querySelector instead of getElementById.

For instance, we write

const id = document.querySelector('[id^="poll-"]').id;

to call querySelector with '[id^="poll-"]' to match the first element where its ID starts with poll-.

Conclusion

To call getElementById based on a partial string with JavaScript, we call querySelector instead of getElementById.

Sometimes, we want to test that a value is greater than or equal to in Jasmine and JavaScript.

In this article, we’ll look at how to test that a value is greater than or equal to in Jasmine and JavaScript.

How to test that a value is greater than or equal to in Jasmine and JavaScript?

To test that a value is greater than or equal to in Jasmine and JavaScript, we can use an expression that has the comparison operator.

For instance, we write

describe("percent", function () {
  it("should be a decimal", () => {
    const percent = insights.percent;

    expect(percent >= 0).toBeTruthy();
    expect(percent).toBeLessThan(1);
  });
});

to check that percent >= 0 is truthy to check that percent is bigger than or equal to 0.

Conclusion

To test that a value is greater than or equal to in Jasmine and JavaScript, we can use an expression that has the comparison operator.

Sometimes, we want to stub a class method with Sinon.js and JavaScript.

In this article, we’ll look at how to stub a class method with Sinon.js and JavaScript.

How to stub a class method with Sinon.js and JavaScript?

To stub a class method with Sinon.js and JavaScript, we can call the sinon.stub method.

For instance, we write

sinon.stub(YourClass.prototype, "myMethod").callsFake(() => {
  return {};
});

to stub the myMethod instance method in the YourClass class.

We call callsFake with a callback that returns the value we want for the fake method.

Likewise, we stub a static method with

sinon.stub(YourClass, "myStaticMethod").callsFake(() => {
  return {};
});

We call stub to stub the YouClass.myStaticMethod static method.

Conclusion

To stub a class method with Sinon.js and JavaScript, we can call the sinon.stub method.