Category: JavaScript

Sometimes, we want to find the time left in a setTimeout() timer with JavaScript.

In this article, we’ll look at how to find the time left in a setTimeout() timer with JavaScript.

How to find the time left in a setTimeout() timer with JavaScript?

To find the time left in a setTimeout() timer with JavaScript, we can use the timer’s _idleStart and _idleTimeout properties.

For instance, we write

const timeout = setTimeout(() => {}, 3600 * 1000);

const getTimeLeft = (timeout) => {
  return Math.ceil(
    (timeout._idleStart + timeout._idleTimeout - Date.now()) / 1000
  );
};

setInterval(() => {
  console.log("Time left: ", getTimeLeft(timeout), "s");
}, 2000);

to create the timeout timer object with setTimeout.

Then we calculate the time left before running the setTimeout callback with the getTimeLeft function.

In it, we use timeout._idleStart + timeout._idleTimeout - Date.now() to compute the time left before the setTimeout callback is run in milliseconds.

Then we divide the ceiling of the number and divide it by 1000 to get the number of seconds.

Next, we call setInterval with a callback that calls getTimeLeft with timeout in the callback to get the number of seconds left before the setTimeout callback is called every 2 seconds.

Conclusion

To find the time left in a setTimeout() timer with JavaScript, we can use the timer’s _idleStart and _idleTimeout properties.

Sometimes, we want to evaluate a string as a mathematical expression in JavaScript.

In this article, we’ll look at how to evaluate a string as a mathematical expression in JavaScript.

How to evaluate a string as a mathematical expression in JavaScript?

To evaluate a string as a mathematical expression in JavaScript, we can use the mathjs library.

To install it, we run

npm install mathjs

Then we can use it by writing

import { evaluate } from "mathjs";

const n = evaluate("1.2 * (2 + 4.5)");

to call evaluate with the math expression we want to evaluate.

The return value is the value of the expression after evaluating as a number.

Conclusion

To evaluate a string as a mathematical expression in JavaScript, we can use the mathjs library.

Sometimes, we want to use getElementsByClassName() with two classes with JavaScript.

In this article, we’ll look at how to use getElementsByClassName() with two classes with JavaScript.

How to use getElementsByClassName() with two classes with JavaScript?

To use getElementsByClassName() with two classes with JavaScript, we can use the querySelectorAll method.

For instance, we write

const els = document.querySelectorAll(".a,.b");

to call document.querySelectorAll to select all elements on the page with classes a and b.

We separate each class with commas in the selector.

Conclusion

To use getElementsByClassName() with two classes with JavaScript, we can use the querySelectorAll method.

Sometimes, we want to remove ‘&quot’ from JSON in JavaScript.

In this article, we’ll look at how to remove ‘&quot’ from JSON in JavaScript.

How to remove ‘&quot’ from JSON in JavaScript?

To remove ‘&quot’ from JSON in JavaScript, we call the string replace method.

For instance, we write

const obj = JSON.parse(data.replace(/"/g, '"'));

to call data.replace with /"/g and '"' to replace all instances of '&quot' with double quotes on the data string.

Then we call JSON.parse to parse the string returned by replace into the obj object.

Conclusion

To remove ‘&quot’ from JSON in JavaScript, we call the string replace method.