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Working with onBlur and onFocus events

From: JavaScript Essential Training

Video: Working with onBlur and onFocus events

Here are two more events, very useful when working with forms. No doubt you've seen this one before. You're filling out a form on a web site and one or more of the fields actually has a value already pre-filled in, perhaps prompting you what to do. You can either click in there or tab into that location and that text will disappear. However, if I tab out of it again, the text comes back to prompt me that I need to put something in there. This is very easy to do using the onfocus and onblur events in JavaScript.

Working with onBlur and onFocus events

Here are two more events, very useful when working with forms. No doubt you've seen this one before. You're filling out a form on a web site and one or more of the fields actually has a value already pre-filled in, perhaps prompting you what to do. You can either click in there or tab into that location and that text will disappear. However, if I tab out of it again, the text comes back to prompt me that I need to put something in there. This is very easy to do using the onfocus and onblur events in JavaScript.

Every one of our form elements here gets an onfocus event kicked off when we click into it, or when we hit the Tab key and tab into it, and when we leave it, that element gets the onblur event. So to create something like this behavior is very simple indeed. Let's take a look at the HTML, then the JavaScript. My HTML is nothing special. I have a form created and I have an input element here for the email, and it has got an ID of email.

And simply, in the JavaScript, Line 2 grabs a hold of a reference to that email field, and then we add two event handlers to it. For my emailField.onfocus we'll execute this function, and for onblur we'll execute this function. So onfocus, meaning we click into it, what it's asking is if the value of that text field is your email, all in lowercase, then we're going to set it to blank and allow someone to type in a value here.

Now, notice that what we're doing when we're trying to grab the contents of the textbox, it's the .value property, not .innerHTML, but .value, and that's the same for pretty much every form field. So the value is your email, we'll blank it out. However, when they leave and we kick off the onblur event, it's going to ask, well, did they leave leaving that value as blank, and if so, what we're going to do is change it right back to your email. So, very easy to do.

if we leave that form field, the value changes to your email. If we click back in, it goes blank. If I type in a value, it will not overwrite it with your email, although that might not be what we want. I'm just checking that they typed something here. If I wanted to write a little bit of code to check it was a valid email format, I could use something called regular expressions, and that's available in JavaScript to do pattern matching. But regular expressions are another movie.

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This video is part of

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JavaScript Essential Training

56 video lessons · 99471 viewers

Simon Allardice
Author

 
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  1. 3m 28s
    1. Welcome
      1m 1s
    2. What you should know
      1m 44s
    3. Using the exercise files
      43s
  2. 15m 41s
    1. Introduction to JavaScript
      8m 6s
    2. Creating your first JavaScript
      2m 13s
    3. Getting to know the tools and applications
      5m 22s
  3. 56m 8s
    1. Understanding the structure of JavaScript code
      7m 9s
    2. Where to write your JavaScript
      3m 56s
    3. Creating variables
      6m 21s
    4. Working with conditional code
      5m 44s
    5. Working with operators
      13m 28s
    6. Sending messages to the console
      2m 59s
    7. Working with loops
      8m 1s
    8. Creating functions
      8m 30s
  4. 36m 13s
    1. Working with arrays
      7m 57s
    2. Working with numbers
      6m 13s
    3. Working with strings
      8m 27s
    4. Working with dates
      5m 38s
    5. Working with objects
      7m 58s
  5. 9m 6s
    1. What is the DOM?
      5m 49s
    2. Working with nodes and elements
      3m 17s
  6. 25m 17s
    1. Accessing DOM elements
      11m 3s
    2. Changing DOM elements
      5m 42s
    3. Creating DOM elements
      8m 32s
  7. 24m 45s
    1. Introduction to JavaScript event handling
      8m 16s
    2. Working with onClick and onLoad events
      7m 36s
    3. Working with onBlur and onFocus events
      2m 36s
    4. Working with timers
      6m 17s
  8. 21m 41s
    1. Common JavaScript errors
      7m 14s
    2. Using Firebug
      4m 7s
    3. Going through a debugging session
      10m 20s
  9. 10m 13s
    1. Accessing form elements
      4m 20s
    2. Preventing a form from being submitted
      2m 36s
    3. Hiding and showing form sections
      3m 17s
  10. 9m 49s
    1. CSS and JavaScript
      3m 46s
    2. Removing and applying CSS classes
      2m 16s
    3. Changing inline styles
      3m 47s
  11. 19m 44s
    1. Understanding JavaScript style
      7m 39s
    2. Minifying your code
      4m 28s
    3. Using JavaScript code checkers
      7m 37s
  12. 22m 24s
    1. Introduction to JavaScript libraries
      3m 17s
    2. Linking to multiple JavaScript files
      2m 11s
    3. Introduction to jQuery
      12m 7s
    4. Using a content distribution network to deliver JavaScript files
      4m 49s
  13. 17m 35s
    1. JavaScript in HTML5
      9m 37s
    2. Using Modernizr
      3m 2s
    3. Using Strict Mode
      4m 56s
  14. 33m 3s
    1. Knowing the JavaScript to avoid
      6m 35s
    2. Introduction to regular expressions
      6m 56s
    3. Working with AJAX
      10m 44s
    4. Working with objects and prototypes
      8m 48s
  15. 21m 10s
    1. Example: Countdown
      8m 3s
    2. Example: Resize
      5m 47s
    3. Example: Accordion
      7m 20s
  16. 4m 58s
    1. Where to go from here
      4m 0s
    2. Goodbye
      58s

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