onsubmit prevents form submission and onclick related operations_javascript skills

1. The return value problem of return. Once there is a return value in the function, 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. function

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 ;
}

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

return true;
}

2. The problem of triggering the onsubmit attribute of the form, what is the onsubmit event? When is it triggered? 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 the following code:

The original onsubmit attribute is like this html A method name of an object, its value (a string) is its method body, and returns true by default;
Like Java, you can write any number of statements in the method body, including built-in functions and custom functions.
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 the event processing function returning false. In most cases, returning false for the event processing function can 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 is equivalent to the terminator, and Return True is equivalent to the executor in js. The function of return false 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), a default event is also triggered, so if you want to. You can return false by canceling the default action of the object. The most common applications of return false are: 1. Hyperlink 2, 3, Content

after the submitAction is executed, 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 and try dragging the image in the IE browser. , you will find that the mouse will become a prohibited operation, and the picture is prohibited from being dragged. It is the default behavior provided by the browser for the mousemove event.
Return false is to remove this behavior, otherwise you will appear. The interrupt events described are executed continuously. In addition, the statement equivalent to return false is:
window.event.returnValue = false,
You can replace return false with this statement and verify it. Finally, please note that this method only applies 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. The occasions where return false is commonly used include:

...

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