Author: John Au-Yeung

Sometimes, we want to determine if user selected a file for file upload with JavaScript.

In this article, we’ll look at how to determine if user selected a file for file upload with JavaScript.

How to determine if user selected a file for file upload with JavaScript?

To determine if user selected a file for file upload with JavaScript, we check if the value property is not an empty string.

For instance, we write

if (document.getElementById("uploadBox").value !== "") {
  // ...
}

to select the file input with getElementById.

And if its value isn’t an empty string, then a file is selected.

Conclusion

To determine if user selected a file for file upload with JavaScript, we check if the value property is not an empty string.

Sometimes, we want to get the currently selected option in a select with JavaScript.

In this article, we’ll look at how to get the currently selected option in a select with JavaScript.

How to get the currently selected option in a select with JavaScript?

To get the currently selected option in a select with JavaScript, we use the selectedIndex property.

For instance, we write

const yourSelect = document.getElementById("your-select-id");
console.log(yourSelect.options[yourSelect.selectedIndex].value);

to select the select element with getElementById.

Then we get the selected option element with yourSelect.options[yourSelect.selectedIndex].

And we get its value attribute value with value.

Conclusion

To get the currently selected option in a select with JavaScript, we use the selectedIndex property.

Sometimes, we want to dynamically creating variables in for loops with JavaScript.

In this article, we’ll look at how to dynamically creating variables in for loops with JavaScript.

How to dynamically creating variables in for loops with JavaScript?

To dynamically creating variables in for loops with JavaScript, we use an array.

For instance, we write

const createVariables = () => {
  const accounts = [];
  for (let i = 0; i <= 20; ++i) {
    accounts[i] = "whatever";
  }
  return accounts;
};

to define the createVariables function.

In it, we loop from i between 0 to 20.

And we use i as the index of the entry we want to put into accounts.

Conclusion

To dynamically creating variables in for loops with JavaScript, we use an array.

Sometimes, we want to use Promise.all with Axios and JavaScript.

In this article, we’ll look at how to use Promise.all with Axios and JavaScript.

How to use Promise.all with Axios and JavaScript?

To use Promise.all with Axios and JavaScript, we call Promise.all with an array of promises returned by Axios.

For instance, we write

const URL1 = "https://www.something.com";
const URL2 = "https://www.something1.com";
const URL3 = "https://www.something2.com";

const promise1 = axios.get(URL1);
const promise2 = axios.get(URL2);
const promise3 = axios.get(URL3);

const values = await Promise.all([promise1, promise2, promise3]);

to call Promise.all with an array with promises returned by axios.get.

Then we get the resolve value of each promise in the values array in the order they’re listed in the array that we called Promise.all with.

Conclusion

To use Promise.all with Axios and JavaScript, we call Promise.all with an array of promises returned by Axios.

Sometimes, we want to set a file name using window.open with JavaScript.

In this article, we’ll look at how to set a file name using window.open with JavaScript.

How to set a file name using window.open with JavaScript?

To set a file name using window.open with JavaScript, we use the download attribute on the link.

For instance, we write

<a href="foo.txt" download="your-foo.txt">Download Your Foo</a>

to set the download attribute to the name of the file we want to download.

The href attribute to the URL of the file.

Conclusion

To set a file name using window.open with JavaScript, we use the download attribute on the link.