Author: John Au-Yeung

Sometimes, we want to generate a random number of fixed length using JavaScript.

In this article, we’ll look at how to generate a random number of fixed length using JavaScript.

How to generate a random number of fixed length using JavaScript?

To generate a random number of fixed length using JavaScript, we can use the Math.floor and Math.random methods.

For instance, we write

console.log(Math.floor(100000 + Math.random() * 900000));

to generate a 6 digit number with

100000 + Math.random() * 900000

Then we get rid of the decimals by returning the floor of the number with Math.floor.

Conclusion

To generate a random number of fixed length using JavaScript, we can use the Math.floor and Math.random methods.

Sometimes, we want to get the position of a div or span tag with JavaScript.

In this article, we’ll look at how to get the position of a div or span tag with JavaScript.

How to get the position of a div or span tag with JavaScript?

To get the position of a div or span tag with JavaScript, we can use the getBoundingClientRect method.

For instance, we write

const offsets = document.getElementById("foo").getBoundingClientRect();
const { top, left } = offsets;

to call getElementById to select the element we want to get the position for.

Then we call getBoundingClientRect on it to get an object with the position values.

And then we can get the top and left position offset with the top and left properties.

Conclusion

To get the position of a div or span tag with JavaScript, we can use the getBoundingClientRect method.

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.