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JavaScript: Enhancing the DOM
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Centering an image


From:

JavaScript: Enhancing the DOM

with Ray Villalobos

Video: Centering an image

So our images are loading, everything is resizing properly. Now it's time to center the images. to do that, I'm going to create a separate function, and it's going to go right down here, right before the closing of the self-executing function. So I'll call this function center image, and this function is going to expect an image to be passed to it. So, what I want to do here is start by creating a couple variables. I'll call this myDifX and that's going to be equal to the window interwidth.
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  1. 2m 36s
    1. Welcome
      59s
    2. What you should know before watching this course
      50s
    3. Using the exercise files
      47s
  2. 24m 33s
    1. What is the Document Object Model (DOM)?
      3m 2s
    2. Navigating the DOM with developer tools
      8m 10s
    3. Testing JavaScript commands with the console
      5m 50s
    4. Communicating with the console through JavaScript
      7m 31s
  3. 31m 9s
    1. Selecting elements with getElementById
      4m 10s
    2. Choosing elements by HTML tag
      3m 20s
    3. Isolating elements by class name
      3m 12s
    4. Querying CSS to select elements
      4m 54s
    5. Working with named form elements
      3m 39s
    6. Understanding nodeType, nodeName, and nodeValue
      4m 30s
    7. Traversing up and down DOM nodes
      4m 40s
    8. Targeting node elements
      2m 44s
  4. 22m 25s
    1. Changing HTML attributes
      5m 25s
    2. Working with restricted attributes
      2m 49s
    3. Detecting data attributes
      3m 29s
    4. Controlling classes with the HTML5 classList
      3m 21s
    5. Targeting the attributes property
      1m 24s
    6. Using text content modifiers
      3m 42s
    7. Modifying elements as text
      2m 15s
  5. 14m 57s
    1. Creating and appending nodes
      4m 27s
    2. Controlling node insertions with insertBefore
      3m 17s
    3. Cloning and removing nodes
      4m 41s
    4. Replacing existing nodes
      2m 32s
  6. 26m 14s
    1. What we'll build
      2m 16s
    2. Adding a bubbling event listener
      4m 11s
    3. Creating and styling an overlay with JavaScript
      4m 39s
    4. Adding an image
      3m 48s
    5. Resizing images in the DOM
      2m 59s
    6. Centering an image
      2m 36s
    7. Handling clicks
      1m 29s
    8. Adjusting for scrolling
      1m 36s
    9. Detecting and adjusting for a window resize
      2m 40s
  7. 1m 49s
    1. Next steps
      1m 49s

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JavaScript: Enhancing the DOM
2h 3m Intermediate Jun 10, 2013

Viewers: in countries Watching now:

The Document Object Model (DOM) is at the core of every HTML page. In order to develop dynamic HTML pages, a front-end developer needs to understand how JavaScript connects to and controls the DOM, allowing you to create, modify, delete, and edit existing page content. This course focuses on helping you understand the DOM elements, and shows the different ways JavaScript gives you access to them and makes it easier to work with the DOM. Author Ray Villalobos covers navigating the DOM, selecting elements, modifying HTML attributes, editing nodes, and much more.

Topics include:
  • What is the DOM?
  • Choosing and isolating elements
  • Traversing up and down DOM nodes
  • Changing HTML attributes
  • Modifying elements as text
  • Creating and appending nodes
  • Cloning and removing nodes
  • Adding a bubbling event listener
  • Adding and resizing images
  • Handling clicks
Subjects:
Developer Web Web Design Web Development
Software:
HTML JavaScript
Author:
Ray Villalobos

Centering an image

So our images are loading, everything is resizing properly. Now it's time to center the images. to do that, I'm going to create a separate function, and it's going to go right down here, right before the closing of the self-executing function. So I'll call this function center image, and this function is going to expect an image to be passed to it. So, what I want to do here is start by creating a couple variables. I'll call this myDifX and that's going to be equal to the window interwidth.

Minus the image that gets past, width, and divided by two. Once we have re-sized, the images they are going to be usually smaller or the same size as the window. So, we need to calculate the difference between the width of the image and the window. Divide that by two so that if it needs to be moved. It's going to be moved by half the distance. That's what places it in the center. So, we'll calculate the difference between the x position and the y position of the images.

So, instead of when or with here this will be inner height, and this will of course be the image height divided by two. Once we have that then we can say the image style, because this is going to be a style sheet attribute that we're changing here. It's going to be equal to, myDifY, plus, because this is CSS, pixels. And then, the same thing for the image left.

And what we'll do here is we'll just return the image. So I'm going to save this, and I need to do one more thing. I need to actually call this function. So, this function will take care of centering an image that passed to it. But of course, I need to call it somewhere. So, I'll do it right before I append the image. So right here, we'll say, center image. And we'll pass it, this, remember that this in this case is going to be the large image.

So, let me save that, go into my page, refresh and click on one of these. Right here, you can see that the image is now in the center of the screen. I'll refresh again and I'll click on any one of these images and they should all be centered. So, I'm refreshing in between. The next thing I need to do is build something. That handles clicking on these images, so the images disappear and I can see my screen again. We'll do that next.

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