First, return as the return keyword, it has the following two ways to return
1. Return control and function results
The syntax is: return expression; the statement ends the function execution, returns the call function, and uses the value of the expression as the result of the function
2. Return control function results
The syntax is: return; in most cases, returning false for event handlers can prevent the default event behavior. For example, by default, clicking on an <A> element will jump to the page specified by the href attribute of the element.
For example:<a href="http:;alert(11);return false;alert(22)" rel="external nofollow" >link</a> <!-- Only alert(11);->
return false is equivalent to the terminator, return true is equivalent to the execution character.
The effect of return false in js is generally used to cancel the default action. For example, if you click a link, in addition to triggering your "onclick" event, you also need to trigger a default event, which is to execute the page jump. So if you want to cancel the default action of the object, you can return false. That is to say, if you want to use JS code to partially change some data without causing changes in other parts of the page, then you should add return false after the onclick event code;
For example:
<input type="submit" onclick="submitAction(); return false;" />
The submitAction method contains the action of submitting the form. If return false is not added, the submit button will continue to execute its default event after executing submitAction and the form will be submitted again. This may be the source of many mistakes.
Indeed, the meaning of return false is not to prevent events from continuing to propagate to top-level elements, but to prevent browsers from processing events by default.
In js, we often use return false to prevent the form from being submitted or continue to execute the following code. In layman's terms, it is to prevent the execution of the default behavior. For example, the following example:
As we all know, addingonsubmit="return false;"Can prevent form submission.
<form action="" method="post" onsubmit="submitTest();"> <INPUT value="www"> <input type="submit" value="submit"></form>
<SCRIPT LANGUAGE="JavaScript"> function submitTest() { // Some logical judgments return false; }
</SCRIPT>
The actual situation of the above code is that the form is submitted normally. If you want it not to submit, you should
<form action="" method="post" onsubmit="submitTest();">
Change to
<form action="" method="post" onsubmit="return submitTest();">
In general, the three situations of return usage in js are summarized as follows:
return true; Return the correct processing result.
return false; return the error processing result; terminate the processing; prevent the form submission; prevent the execution of the default behavior.
return; return control to the page.
Summarize
The above is the usage and principle analysis of the return boolean value in JavaScript introduced to you by the editor. I hope it will be helpful to you. If you have any questions, please leave me a message and the editor will reply to you in time. Thank you very much for your support for my website!