Usage of return false (block) in js_jquery-JS Tutorial-php.cn

Usage of return false (block) in js_jquery

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Release： 2016-05-16 17:25:45

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return false prevents form submission. This problem has troubled me for a long time today. I found a lot of information on the Internet. Basically, there are the following points to note about onsubmit=return false:

1. The return value of return The problem is, once there is a return value in the function return, the following statement will not be executed, but will jump directly to the place where the function is called. In the following PHP function code, if the first if condition is met, the function value returns Boolean false. You can return the value of a function and jump out of the function; as long as the return statement is encountered, the program will stop executing on that line of code, and the execution control will immediately Return to the code that called the program.

Copy code The code is as follows:

 
function chkinput(form) 
{ 
 if(form.title.value=="") 
{ 
alert("Please enter the article title!"); 
form.title.select(); 
return false; //Note It cannot be written as return(false); 2009.12.15 
} 

if(form.content.value=="") 
{ 
alert("The article text cannot be empty@!! "); 
form.content.select(); 
return false; 
} 

return true; 
} 

2.form The problem of triggering the onsubmit attribute, when does the onsubmit event trigger? The onsubmit event occurs when the confirm button in the form is clicked. The reasons for not triggering are generally as follows:

A. The triggering time of the onsubmit attribute is when the form is submitted with a button such as input:submit, otherwise it will not be triggered. If you use a normal input:button, specify a javascript function in the onclick attribute, and execute the submit() function of the form in this function instead of the onsubmit attribute.

B. First look at a piece of code:

Copy the code The code is as follows:

Click the submit button and the form is not submitted. Because there is one place that should be changed to (red font)
It turns out that the onsubmit attribute is like the

html object A method name, its value (a string) is its method body, and returns true by default;

Same as Java, you can write any number of statements in the method body, including built-in functions and custom function.

Although submitTest() returns false here, we only executed this function without any processing of its results.

And onsubmit="return submitTest() uses its return value to achieve the expected effect.

3. The problem of event processing functions returning false, in most cases, is the event The handler function returns false to prevent the default event behavior.

For example, by default, clicking an element will jump to the page specified by the href attribute of the element.
Return False Equivalent to the terminator, Return True is equivalent to the executor. The function of return false in js is generally used to cancel the default action. For example, when you click a link, it will trigger your
onclick time. If specified), a default event will be triggered, which is to execute the page jump. So if
you want to cancel the default action of the object, you can return false. Return false is often used in:

<.>

Copy code The code is as follows:

1, Hyperlink
2,
3.
Content

The submitAction method contains the action of submitting the form. If. Without return false,

After executing submitAction, the submit button will continue to execute its default event and the form will be submitted again. This may be the source of many errors.
Indeed, the meaning of return false is not to prevent the event from continuing to propagate to the top-level element, but to prevent the browser from handling the event by default. You can try this:
First comment out all the js scripts, try dragging the image in the IE browser, you will find that the mouse will become a prohibited operation style, the image is prohibited from dragging, it is browsing The default behavior provided by the controller for the mousemove event.

Return false is to remove this behavior, otherwise the interruption event you described will occur and continue to execute.
In addition, the equivalent statement to return false is:

window.event.returnValue = false,
You can replace return false with this statement and verify it.
Finally, this method is only applicable to IE browser.

The function of return false in js is generally used to cancel the default action. For example, when you click a link, in addition to triggering your
onclick time (if you specify it), it also triggers a default event, which is to execute a page jump. So if
you want to cancel the default action of the object, you can return false. There are many occasions where return false is used:

Copy code The code is as follows:

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