Category: JavaScript

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Vue Answers

How to Listen to the Window Scroll Event in a Vue.js Component with JavaScript?

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Sometimes, we want to listen to the window scroll event in a Vue.js component with JavaScript.

In this article, we’ll look at how to listen to the window scroll event in a Vue.js component with JavaScript.

Listen to the Window Scroll Event in a Vue.js Component

We can listen to the window scroll event in a Vue.js component by calling the window.addEventListener method to listen to the scroll event on the browser window.

For instance, we can write:

<template>
  <div id="app">
    <p v-for="n of 100" :key="n">{{ n }}</p>
  </div>
</template>

<script>
export default {
  name: "App",
  created() {
    window.addEventListener("scroll", this.handleScroll);
  },
  destroyed() {
    window.removeEventListener("scroll", this.handleScroll);
  },
  methods: {
    handleScroll(event) {
      console.log(window.scrollY);
    },
  },
};
</script>

We call window.addEventListener with 'scroll' in the created hook to add the handleScroll scroll event listener when the component is mounted.

And in the destroyed hook, we call window.renmoveListener to remove the handleScroll scroll event listener.

In the handleScroll method, we have the window.scrollY property to get the vertical scroll position.

In the template, we have some scrollable content. If we scroll through it, we should see the scrollY value logged.

Conclusion

We can listen to the window scroll event in a Vue.js component by calling the window.addEventListener method to listen to the scroll event on the browser window.

Categories
Vue Answers

How to Scroll to an Element with Vue.js and JavaScript?

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Sometimes, we want to scroll to an element with Vue.js and JavaScript.

In this article, we’ll look at how to scroll to an element with Vue.js and JavaScript.

Scroll to an Element with Vue.js and JavaScript

We can scroll to an element with Vue.js by assigning a ref to the element we want to scroll to.

Then we can scroll to the element by calling the scrollIntoView method on the element assigned to the ref.

For instance, we can write:

<template>
  <div id="app">
    <button @click="scrollToElement">scroll to last</button>
    <p v-for="n of 100" :key="n" :ref="n === 100 ? 'last' : undefined">
      {{ n }}
    </p>
  </div>
</template>

<script>
export default {
  name: "App",
  methods: {
    scrollToElement() {
      const [el] = this.$refs.last;
      if (el) {
        el.scrollIntoView({ behavior: "smooth" });
      }
    },
  },
};
</script>

We have the scroll to last button that calls scrollToElement .

Then we have some p element with the last ref being assigned to the last p element.

In the scrollToElement method, we get the element assigned to the last ref with this.$refs.last via destructuring.

Then we call el.scrollIntoView with an object that has the behavior property to change the scroll behavior.

Conclusion

We can scroll to an element with Vue.js by assigning a ref to the element we want to scroll to.

Then we can scroll to the element by calling the scrollIntoView method on the element assigned to the ref.

Categories
JavaScript Answers

How to Search for the Immediate Children of an Element Returned by querySelector with JavaScript?

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Sometimes, we want to search for the immediate children of an element returned by querySelector with JavaScript.

In this article, we’ll look at how to search for the immediate children of an element returned by querySelector with JavaScript.

Search for the Immediate Children of an Element Returned by querySelector

To search for the immediate children of an element returned by document.querySelector , we can use the :scope pseudoselector.

For instance, if we have the following HTML:

<div>  
  <p>  
    hello world  
  </p>  
</div>

Then we can get the p element given the div by writing:

const getChild = (elem) => {  
  return elem.querySelectorAll(':scope > p');  
};  
const div = document.querySelector('div')  
console.log(getChild(div))

We define the getChild function that calls elem.querySelectorAll to get all the p elements that are the immediate child of the given elem .

Then we get the div with querySelector and assign it to div .

And then we call getChild with div to get the p element in the div in a Nodelist.

Conclusion

To search for the immediate children of an element returned by document.querySelector , we can use the :scope pseudoselector.

Categories
JavaScript Answers

How to Fill the Whole Canvas with a Specific Color in JavaScript?

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Sometimes, we want to fill the whole canvas with a specific color in JavaScript.

In this article, we’ll look at how to fill the whole canvas with a specific color in JavaScript.

Fill the Whole Canvas with a Specific Color in JavaScript

To fill the whole canvas with a specific color in JavaScript, we can set the glovalCompositionOperation property of the canvas context to 'destination-cover' .

Then we can set the fillStyle to the color we want to fill the canvas with.

For instance, we can write:

<canvas width='300' height='300'></canvas>

to add the canvas.

Then we write:

const canvas = document.querySelector("canvas");  
const ctx = canvas.getContext("2d");  
ctx.globalCompositeOperation = 'destination-over'  
ctx.fillStyle = "blue";  
ctx.fillRect(0, 0, canvas.width, canvas.height);

We get the canvas with document.querySelector .

Then we get the context with getContext .

Then we set the glovalCompositionOperation property of the canvas context to 'destination-cover' to add the color behind other elements.

Next, we set fillStyle to 'blue' to make the canvas blue.

And then we call fillRect to add the fill color to the canvas.

Conclusion

To fill the whole canvas with a specific color in JavaScript, we can set the glovalCompositionOperation property of the canvas context to 'destination-cover' .

Then we can set the fillStyle to the color we want to fill the canvas with.

Categories
JavaScript Answers

How to Use querySelector with IDs that are Numbers in JavaScript?

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Sometimes, we want to use querySelector with IDs that are numbers in JavaScript.

In this article, we’ll look at how to use querySelector with IDs that are numbers in JavaScript.

Use querySelector with IDs that are Numbers in JavaScript

To use querySelector with IDs that are numbers in JavaScript, we have to escape the unicode code point representation of the number.

For instance, we can write:

<div id='1'>
  hello world
</div>

Then we write:

const el = document.querySelector('#\\31');
console.log(el)

to select the div with ID 1.

U+0031 is the Unicode code point of the character 1, so we pass in \31 , which is the escaped version of the Unicode code point representation of 1.

el should be the div with ID 1 as a result.

Conclusion

To use querySelector with IDs that are numbers in JavaScript, we have to escape the unicode code point representation of the number.