Author: John Au-Yeung

Sometimes, we want to reverse a string in JavaScript.

In this article, we’ll look at how to reverse a string in JavaScript.

How to reverse a string in JavaScript?

To reverse a string in JavaScript, we use the string split and array reverse and join methods.

For instance, we write

const reversedStr = str.split("").reverse().join("");

to call str.split to split the string into an array of characters.

Then we call reverse to return a reversed version of the array.

And then we call join to combine the characters in the reversed array and return the string.

Conclusion

To reverse a string in JavaScript, we use the string split and array reverse and join methods.

Sometimes, we want to find the number of occurrences a given value has in an array with JavaScript.

In this article, we’ll look at how to find the number of occurrences a given value has in an array with JavaScript.

How to find the number of occurrences a given value has in an array with JavaScript?

To find the number of occurrences a given value has in an array with JavaScript, we use the array filter method.

For instance, we write

const dataset = [2, 2, 4, 2, 6, 4, 7, 8];
const search = 2;
const occurrences = dataset.filter((val) => {
  return val === search;
}).length;
console.log(occurrences);

to call datset.filter with a callback that checks if val in dataset is the same as search and return an array where all the values are equal to search.

Then we get the length property to get the number of items equal to search.

Conclusion

To find the number of occurrences a given value has in an array with JavaScript, we use the array filter method.

Sometimes, we want to call a method from another method in the same class with JavaScript.

In this article, we’ll look at how to call a method from another method in the same class with JavaScript.

How to call a method from another method in the same class with JavaScript?

To call a method from another method in the same class with JavaScript, we use this.

For instance, we write

class MyClass {
  myTest() {
    console.log("it works");
  }

  runMyTest() {
    this.myTest();
  }
}

const myClass = new MyClass();
myClass.runMyTest();

to call this.myTest in runMyTest to call the myTest method in runMyTest.

Conclusion

To call a method from another method in the same class with JavaScript, we use this.

Sometimes, we want to attach ‘onclick’ event to D3 chart background with JavaScript.

In this article, we’ll look at how to attach ‘onclick’ event to D3 chart background with JavaScript.

How to attach ‘onclick’ event to D3 chart background with JavaScript?

To attach ‘onclick’ event to D3 chart background with JavaScript, we call the on method.

For instance, we write

rect.on("click", () => {
  console.log("rect");
  d3.event.stopPropagation();
});

to call on with 'click to add a click listener to the rect object.

In the event listener, we call stopPropagation to stop the event from bubbling up.

Conclusion

To attach ‘onclick’ event to D3 chart background with JavaScript, we call the on method.

To change ISO date string to Date object with JavaScript, we use moment.js.

For instance, we write

const d = moment("2022-11-03T19:38:34.203Z", "YYYY-MM-DD HH:mm").toDate();

to call moment with the ISO date string and the date format to parse the date into a moment object that has the date in UTC.

Then we call toDate to convert it to a JavaScript date object.