referencing functions and calling functions
Here, when the function is specified as a handler, the following parentheses are omitted and only the function name is used. With parentheses, the function is called immediately; without parentheses, the function name is simply a function identifier or a reference to a function that can be used to invoke the function in the future.
This raises my mind about the way the binding event works. We all know that when binding an event handler for an element, the inline way is to write <body onload= "dosomething ();" >...</ Body > , or JavaScript code to write like this
1 window.onload=dosomething;//or the next line way 2 window.addeventlistener (' Load ', dosomething, false ); 3 function dosomething () {4 ... 5 }We have always used this, but have not thought about why the onload= "dosomething ( )" To add "()"? Can I give it no? , and the JS code of onload and AddEventListener Why not Add "()", I can add it to it?
1. In the standard inline mode, the console will output "test" as promised.
1 <!DOCTYPE HTML>2 <HTML>3 <Head>4 <title></title>5 </Head>6 <Bodyonload= "dosomething ()">7 <Scripttype= "Text/javascript">8 functiondosomething () {9 Console.log ('Test');Ten } One </Script> A </Body> - </HTML>
2. Inline mode does not add "()"
1 <!DOCTYPE HTML>2 <HTML>3 <Head>4 <title></title>5 </Head>6 <Bodyonload= "DoSomething">7 <Scripttype= "Text/javascript">8 functiondosomething () {9 Console.log ('Test');Ten } One </Script> A </Body> - </HTML>
The result console does not output and does not prompt the error, to break the point to see what happened to the program, to the main code each line to break the breakpoint
Then rerun the program, the program to line 6th, pause.
Click Continue execution, the program does not execute the 9th line of code but run directly finished. And then look at the document.body.onload property Output is
So this means that when the onload event is triggered, the function onload is executed, the contents of which are dosomething , not dosomething. () , so the onload event does not execute after the something function is triggered just after the trigger enters function onload and ends.
3. Standard JS binding event mode, Window.onload and AddEventListener, the former example
referencing functions, calling functions, revealing
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