Category: JavaScript

Sometimes, we want to use Jest to spy on a method call with JavaScript.

In this article, we’ll look at how to use Jest to spy on a method call with JavaScript.

How to use Jest to spy on a method call with JavaScript?

To use Jest to spy on a method call with JavaScript, we call the spyOn method.

For instance, we write

const spy = jest.spyOn(Component.prototype, "methodName");
const wrapper = mount(<Component {...props} />);
wrapper.instance().methodName();
expect(spy).toHaveBeenCalled();

in our test to call spyOn to add a spy to the Component‘s methodName instance method.

The we call the methodName method on the component.

And we check if it’s called with with toHaveBeenCalled.

Conclusion

To use Jest to spy on a method call with JavaScript, we call the spyOn method.

Sometimes, we want to split and modify a string in Node.js and JavaScript.

In this article, we’ll look at how to split and modify a string in Node.js and JavaScript.

How to split and modify a string in Node.js and JavaScript?

To split and modify a string in Node.js and JavaScript, we use the split and map methods.

For instance, we write

const str = "123, 124, 234,252";
const arr = str.split(",").map((val) => Number(val) + 1);
console.log(arr);

to call str.split to split the string into a string array by the comma.

Then we call map with a callback to map each value to the value we want.

Conclusion

To split and modify a string in Node.js and JavaScript, we use the split and map methods.

Sometimes, we want to toggle display: none style with JavaScript.

In this article, we’ll look at how to toggle display: none style with JavaScript.

How to toggle display: none style with JavaScript?

To toggle display: none style with JavaScript, we set the style.display property.

For instance, we write

const yourUl = document.getElementById("yourUlId");
yourUl.style.display = yourUl.style.display === "none" ? "" : "none";

to select the element to modify with getElementById.

Then we set its style.display property to '' is it’s currently 'none'.

Otherwise, we set it to 'none'.

Conclusion

To toggle display: none style with JavaScript, we set the style.display property.

To flatten an array of arrays of objects with JavaScript, we use the array flat method.

For instance, we write

const flattenedArr = [["object1"], ["object2"]].flat();

to return a flattened version of the nested array with flat.

Conclusion

To flatten an array of arrays of objects with JavaScript, we use the array flat method.