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Introduction to return statement in javascript

怪我咯Original: 2017-07-16 10:45:371577browse

The return statement is very important in js. It is executed at the end of the function statement and returns the value of expression as the result of the function; it not only has the function of returning the function value, There are also some special usages, and it is very necessary to have a clear grasp. Let's briefly introduce the function of the return statement with examples.

1. Used to return control and function results:

Usually, the return statement is necessary for a function, because the function is often required in a series of After the code is executed, an expected return value will be obtained, and this value is returned through the return statement, and control is returned to the calling function.

Grammar format:

return Expression

The code example is as follows:

function add(){
 var a=1;
 var b=2;
 return a+b;
}
function func(){
 console.log(add())
}
func();

The above code , when the func() function is called, the control is held by the func function. When the add function is called again, the control is handed over to the add function, and then a value is returned and the control is handed over to the func function.
Usually return is followed by an expression, but it is not absolute. For example:

return;

In this case, the control is simply transferred to the main caller. The function continues execution.

There is nothing special about the ordinary application of the return statement. The most important thing to note is the use of return false. Event processingThe function returns false to prevent the occurrence of the default event.
The code example is as follows:

<!DOCTYPE html> 
<html> 
<head> 
<meta charset=" utf-8"> 
<title>脚本之家</title> 
<script type="text/javascript"> 
window.onload=function(){ 
 var olink=document.getElementById("thelink"); 
 olink.onclick=function(){
  return false
 } 
} 
</script> 
</head> 
<body> 
<a href="" id="thelink">脚本之家</a> 
</body> 
</html>

The onclick event will occur when a link is clicked. Its default action is that the link points to the link specified by the href attribute, but if the event handler uses return false, it will be blocked. The default event occurs.
return false can also prevent event bubbling from occurring.

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