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4-7. Checking Whether a Checkbox Is Checked
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You have several checkboxes, where each designates an item being sold in a food court. You want to confirm that at least one of the checkboxes is checked when selecting the Submit button. If none of the checkboxes is selected, you want to display an error message.
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Solution
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Let us make an HTML file that displays four checkboxes, an error message, and an empty paragraph element for displaying the result (total bill of the food items selected). The HTML file may appear as shown here: <body> <form> <input type="checkbox" id="pizza" name="pizza" value=5 class="infobox">Pizza $5 <br> <input type="checkbox" id="hotdog" name="hotdog" value=2 class="infobox">HotDog $2<br> <input type="checkbox" id="coke" name="coke" value=1 class="infobox">Coke $1<br> <input type="checkbox" id="fries" name="fries" value=3 class="infobox">French Fries $3<br> <p class="error">Select at least one checkbox </p> <p class="result"></p> <input class="submit" type="submit" value="Submit"> </form> </body> The class selectors to apply the style properties automatically to the HTML elements are defined in the external style sheet style.css, which may appear as shown here: style.css .infobox { margin-top: 15px; } .error { color: red; } The jQuery code to see whether a checkbox is checked or not is as shown here: $(document).ready(function() { $('.error').hide(); $('.submit').click(function(event){ var count=0; var amt=0;
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$('form').find(':checkbox').each(function(){ if($(this).is(':checked')) { count++; amt=amt+parseInt($(this).val()); } }); if(count==0) { $('p.result').hide(); $('.error').show(); } else { $('.error').hide(); $('p.result').show(); $('p.result').text('Your bill is $ '+amt); } event.preventDefault(); }); });
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In the following jQuery code we confirm whether any of the checkboxes are checked before using the loop to inspect each of them individually: $(document).ready(function() { $('.error').hide(); $('.submit').click(function(event){ var amt=0; var count=$('input:checked').length; if(count==0) { $('p.result').hide(); $('.error').show(); } else { $('form').find(':checkbox').each(function(){ if($(this).is(':checked')) { amt=amt+parseInt($(this).val()); } }); $('.error').hide(); $('p.result').show(); $('p.result').text('Your bill is $ '+amt); }
CHAPTER 4 FORM VALIDATION
event.preventDefault(); }); });
How It Works
In the HTML file, we can see that the four checkboxes are assigned the class name infobox and represent the four items sold in a food court pizza, hotdog, Coke, and French fries along with their price. The paragraph element to display the error message is assigned the class name error and its text displays the error message Select at least one checkbox. There is one more paragraph element to display the bill of the food items selected via checkboxes, and it is assigned the class name result and is currently empty. It will be assigned the text to display the bill via jQuery code. The style sheet defines two class selectors: infobox to be applied to the checkboxes, and the class selector error to be applied to the paragraph element that is meant for displaying the error message. The infobox class selector contains the property margin-top set to 15px to create a sufficient vertical gap among the checkboxes being displayed. The class selector error contains the style property color set to value red so that the error message appears in red (so that it appears highlighted) In the jQuery code, we first set the error message to be invisible. Then we attach a click event to the Submit button. On selecting the Submit button, its event-handling function will be executed that will do several tasks. In the event-handling function, we first initialize a counter count set to value 0 (which will be used for counting the number of checkboxes that are checked) and another variable amt set to 0 that will be used for totaling the bill of the food items selected. Using the .each() function, we check all the checkboxes of the form one by one and if any of the checkbox is found checked, we increment the value of the counter variable count by 1 and the amount of that food item is added to the amt variable. That is, we are setting the count of the checked checkboxes in the count variable and the total amount of the selected checkboxes in the amt variable. After inspecting all the checkboxes, if we find that the value of the count variable is 0, meaning none of the checkbox is selected, we make the paragraph element meant for displaying the error message visible to display Select at least one checkbox on the screen. If the value of the count variable is not 0 (meaning at least one of the checkboxes is selected), we make the paragraph element of the class result visible (and hide the paragraph of the class error) and assign the following text to it: Your bill is $ +amt, where amt is the variable in which the total amount for the food items selected is stored. If we select none of the checkboxes and select the Submit button, an error message Select at least one checkbox will appear on the screen, as shown in Figure 4-15.
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