Category: JavaScript

Categories
Vue Answers

How to watch props change with Vue Composition API and Vue 3?

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Sometimes, we want to watch props change with Vue Composition API and Vue 3.

In this article, we’ll look at how to watch props change with Vue Composition API and Vue 3.

How to watch props change with Vue Composition API and Vue 3?

To watch props change with Vue Composition API and Vue 3, we can use the watch function.

For instance, we write

watch(() => props.selected, (selection, prevSelection) => { 
   /* ... */ 
})

to call watch to watch the selected prop.

We get the latest and previous value of it from the parameters in the 3rd argument.

Also, we can also put the prop in a ref and watch the ref with

const selected = ref(props.selected);

watch(selected, (selection, prevSelection) => {
  /* ... */
});

And we can watch multiple refs with

watch([ref1, ref2], ([refVal1, refVal2], [prevRef1, prevRef2]) => {
  /* ... */
});

Conclusion

To watch props change with Vue Composition API and Vue 3, we can use the watch function.

Categories
JavaScript Answers

How to append child after element with JavaScript?

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Sometimes, we want to append child after element with JavaScript.

In this article, we’ll look at how to append child after element with JavaScript.

How to append child after element with JavaScript?

To append child after element with JavaScript, we can use the insertBefore method.

For instance, we write

if (parentGuest.nextSibling) {
  parentGuest.parentNode.insertBefore(childGuest, parentGuest.nextSibling);
} else {
  parentGuest.parentNode.appendChild(childGuest);
}

to call parentGuest.parentNode.insertBefore to insert childGuest before parentGuest element’s next sibling to insert it after parentGuest if nextSibling exists.

Otherwise, we insert it as its last child with appendChild.

Conclusion

To append child after element with JavaScript, we can use the insertBefore method.

Categories
JavaScript Answers

How to get first three characters of a string with JavaScript?

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Sometimes, we want to get first three characters of a string with JavaScript.

In this article, we’ll look at how to get first three characters of a string with JavaScript.

How to get first three characters of a string with JavaScript?

To get first three characters of a string with JavaScript, we can use the string substring method.

For instance, we write

const str = "012123";
const strFirstThree = str.substring(0, 3);

console.log(strFirstThree);

to call str.substring with 0 and 3 to return a string with the first 3 characters of str.

Conclusion

To get first three characters of a string with JavaScript, we can use the string substring method.

Categories
TypeScript Answers

How to cast int to enum strings in TypeScript?

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Sometimes, we want to cast int to enum strings in TypeScript.

In this article, we’ll look at how to cast int to enum strings in TypeScript.

How to cast int to enum strings in TypeScript?

To cast int to enum strings in TypeScript, we can use square brackets.

For instance, we write

export enum Type {
  Info,
  Warning,
  Error,
  Fatal,
}

to define the Type enum.

Then we use Type[Type.Info] to return type 'Info'.

Conclusion

To cast int to enum strings in TypeScript, we can use square brackets.

Categories
JavaScript Answers

How to modify object property in an array of objects with JavaScript?

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Sometimes, we want to modify object property in an array of objects with JavaScript.

In this article, we’ll look at how to modify object property in an array of objects with JavaScript.

How to modify object property in an array of objects with JavaScript?

To modify object property in an array of objects with JavaScript, we can use the array find method.

For instance, we write

const foo = [
  { bar: 1, baz: [1, 2, 3] },
  { bar: 2, baz: [4, 5, 6] },
];

const obj = foo.find((f) => f.bar == 1);
if (obj) {
  obj.baz = [2, 3, 4];
}

console.log(foo);

to define the foo array.

Then we call foo.find with a callback to return the object in foo with bar set to 1.

If obj isn’t undefined, then we set obj.baz to a new value.

Conclusion

To modify object property in an array of objects with JavaScript, we can use the array find method.