Category: JavaScript

Sometimes, we want to fix using forEach on an array from getElementsByClassName results in “TypeError: undefined is not a function” error with JavaScript.

In this article, we’ll look at how to fix using forEach on an array from getElementsByClassName results in “TypeError: undefined is not a function” error with JavaScript.

How to fix using forEach on an array from getElementsByClassName results in “TypeError: undefined is not a function” error with JavaScript?

To fix using forEach on an array from getElementsByClassName results in “TypeError: undefined is not a function” error with JavaScript, we can use the spread operator to convert the node list returned by getElementsByClassName to an array.

For instance, we write

[...document.getElementsByClassName("myClass")].forEach((v) => {
  //...
});

to get the elements with class myClass with getElementsByClassName.

Then we spread the entries in the node list returned by getElementsByClassName into an array.

Next, we call forEach with a callback to loop through each element.

Conclusion

To fix using forEach on an array from getElementsByClassName results in “TypeError: undefined is not a function” error with JavaScript, we can use the spread operator to convert the node list returned by getElementsByClassName to an array.

Sometimes, we want to create Mongoose schema with an array of object IDs with JavaScript.

In this article, we’ll look at how to create Mongoose schema with an array of object IDs with JavaScript.

How to create Mongoose schema with an array of object IDs with JavaScript?

To create Mongoose schema with an array of object IDs with JavaScript, we can set schema property to an array of objects that specifies that the field is an array of object IDs.

For instance, we write

const userSchema = mongoose.Schema({
  email: { type: String, required: true, unique: true },
  password: { type: String, required: true },
  name: {
    first: { type: String, required: true, trim: true },
    last: { type: String, required: true, trim: true },
  },
  phone: Number,
  lists: [listSchema],
  friends: [{ type: ObjectId, ref: "User" }],
  accessToken: { type: String },
});

exports.User = mongoose.model("User", userSchema);

to create the userSchema that has the friends field that holds an array of object IDs by setting friends to [{ type: ObjectId, ref: "User" }].

We specifies that each friends entry references the object ID of a User.

Conclusion

To create Mongoose schema with an array of object IDs with JavaScript, we can set schema property to an array of objects that specifies that the field is an array of object IDs.

Sometimes, we want to reload CSS without reloading the page with JavaScript.

In this article, we’ll look at how to reload CSS without reloading the page with JavaScript.

How to reload CSS without reloading the page with JavaScript?

To reload CSS without reloading the page with JavaScript, we can loop through the link elements and update their href attribute values.

For instance, we write

const reloadCss = () => {
  const links = document.getElementsByTagName("link");
  for (const link of links) {
    if (link.rel === "stylesheet") {
      link.href += "";
    }
  }
};

to define the reloadCss function.

In it, we get all the link elements with getElementsByTagName.

Then we loop through the links with a for-of loop.

In it, we check if the rel attribute of each link is 'stylesheet' with

link.rel === "stylesheet"

If it is, then we update the href attribute with

link.href += ""

to reload the CSS referenced by the link element.

Conclusion

To reload CSS without reloading the page with JavaScript, we can loop through the link elements and update their href attribute values.

Sometimes, we want to convert Moment.js date to users local time zone with JavaScript.

In this article, we’ll look at how to convert Moment.js date to users local time zone with JavaScript.

How to convert Moment.js date to users local time zone with JavaScript?

To convert Moment.js date to users local time zone with JavaScript, we can use the local method.

For instance, we write

const testDateUtc = moment.utc("2022-01-30 10:00:00");
const localDate = moment(testDateUtc).local();

to create a moment UTC datetime object with moment.utc.

Then we call moment with testDateUtc to create a new moment object.

Finally, we call local on it to return testDateUtc converted to the local time zone.

Conclusion

To convert Moment.js date to users local time zone with JavaScript, we can use the local method.

Sometimes, we want to change the behavior of a mocked import with Jest and JavaScript.

In this article, we’ll look at how to change the behavior of a mocked import with Jest and JavaScript.

How to change the behavior of a mocked import with Jest and JavaScript?

To change the behavior of a mocked import with Jest and JavaScript, we call the jest.mock method.

For instance, we write

import { methodToMock } from "the-package-to-mock";

jest.mock("the-package-to-mock", () => ({
  methodToMock: jest.fn(),
}));

it("test1", () => {
  methodToMock.mockImplementation(() => "someValue");
});

it("test2", () => {
  methodToMock.mockImplementation(() => "anotherValue");
});

to call jest.mock to mock the methodToMock method in the the-package-to-mock module.

We set methodToMock to the mock function returned by jest.fn.

Then in our tests, we call methodToMock.mockImplementation with a callback mocks the behavior of methodToMock.

Conclusion

To change the behavior of a mocked import with Jest and JavaScript, we call the jest.mock method.