Category: JavaScript Answers

Sometimes, we want to check for IP addresses with JavaScript.

In this article, we’ll look at how to check for IP addresses with JavaScript.

How to check for IP addresses with JavaScript?

To check for IP addresses with JavaScript, we use the is-ip module.

We install it with

npm i is-ip

Then we use it by writing

const isIp = require("is-ip");

const isItIp = isIp("192.168.0.1");

to call isIp with a string that we want to check if it’s a string with an IP address.

Conclusion

To check for IP addresses with JavaScript, we use the is-ip module.

Sometimes, we want to get the max value of scrollLeft with JavaScript.

In this article, we’ll look at how to get the max value of scrollLeft with JavaScript.

How to get the max value of scrollLeft with JavaScript?

To get the max value of scrollLeft with JavaScript, we can use the scrollWidth and clientWidth propeties.

For instance, we write

const maxScrollLeft = element.scrollWidth - element.clientWidth;

to subtract the element‘s scrollWidth value by its clientWidth value.

Then we get the max value of scrollLeft.

Conclusion

To get the max value of scrollLeft with JavaScript, we can use the scrollWidth and clientWidth propeties.

Sometimes, we want to add an img element to a div with JavaScript.

In this article, we’ll look at how to add an img element to a div with JavaScript.

How to add an img element to a div with JavaScript?

To add an img element to a div with JavaScript, we use the appendChild method.

For instance, we write

document.getElementById("placehere").appendChild(elem);

to get the element with ID placehere with getElementById.

Then we call appendChild to add the elem img element as the last child of the element with ID placehere.

Conclusion

To add an img element to a div with JavaScript, we use the appendChild method.

Sometimes, we want to mock inner function with Jest and JavaScript.

In this article, we’ll look at how to mock inner function with Jest and JavaScript.

How to mock inner function with Jest and JavaScript?

To mock inner function with Jest and JavaScript, we should export the inner function in a module.

For instance, we write

funcB.js

export const funcB = () => {
  return "original";
};

Then we import it with

foo.js

import { funcB } from "./funcB";

export const funcA = () => {
  return funcB();
};

Next, we write tests for funcA and funcB with

import * as funcBModule from "./funcB";
import { funcA } from "./foo";

describe("helper", () => {
  test("test funcB", () => {
    expect(funcBModule.funcB()).toBe("original");
  });

  test("test funcA", () => {
    const spy = jest.spyOn(funcBModule, "funcB");
    spy.mockReturnValue("mocked");

    expect(funcA()).toBe("mocked");

    spy.mockRestore();
  });
});

We funcBModule.funcB in the first test.

And we create a spy and mock the return value of funcB in the 2nd test with

const spy = jest.spyOn(funcBModule, "funcB");
spy.mockReturnValue("mocked");

And we call funcA after that.

Finally we call mockRestore to restore the mocks to their original values.

Conclusion

To mock inner function with Jest and JavaScript, we should export the inner function in a module.

Sometimes, we want to get the difference between dates in JavaScript.

In this article, we’ll look at how to get the difference between dates in JavaScript.

How to get the difference between dates in JavaScript?

To get the difference between dates in JavaScript, we can subtract 2 date objects directly.

For instance, we write

const a = new Date();
const b = new Date(2022, 0, 1, 0, 0, 0, 0);
const d = b - a;

to define the a and b date objects.

Then we subtract b by a to get their difference.

They’ll be converted to timestamps in milliseconds before the difference is computed, so d would be a timestamp in milliseconds.

Conclusion

To get the difference between dates in JavaScript, we can subtract 2 date objects directly.