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hisoka

By hisoka
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davej Devoted Member

davej

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fnd and init are both functions so why we did not write them like this

 

document.getElementById('btn1').onclick = fnd();window.onload = init();

 

Because that doesn't work. Try it and see for yourself.

 

<script>

'use strict';x = 3.14; function show[]{return x +10 ;} </script>

 

I see errors:

SyntaxError: missing ( before formal parameters

ReferenceError: assignment to undeclared variable x

<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"/><title>title</title><script>window.onerror = function(a, b, c, d){alert('Javascript Error:n'+a+'nURL: '+b+'nLine: '+c+'  Column: '+d);return true;}</script><script>'use strict';x = 3.14;function show[]{return x +10 ;}</script></head><body></body>    </html>
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hisoka Invested Member

hisoka

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Sorry but I did not ask what is the difference between :

 

 

document.getElementById('btn1').onclick = fnd();window.onload = init();

 

and this :

 

document.getElementById('btn1').onclick = fnd;window.onload = init;

 

my question was why we did not use the parenthesis in

 

document.getElementById('btn1').onclick = fnd;window.onload = init;

 

this answer

 

"This line:window.onload = init;Tells it to assign the function init to the window.onload handler. This line:window.onload = init();Tells it to execute the function init and assign the return value of that function to the window.onload handler. If init does not return a function then that will be a problem."

 

is about the logic that drives the code . However , my question was about the syntax and

 

Syntactically , why we used init in window.onload = init; and fnd in document.getElementById('btn1').onclick = fnd; without parenthesis ??

 

 

"Are you sure about that?" yes I am sure

 

 

I ran this script :

 

<script>'use strict';x = 3.14; function show[]{return x +10 ;} </script>

 

I did not include this :

 

window.onerror = function(a, b, c, d){alert('Javascript Error:n'+a+'nURL: '+b+'nLine: '+c+' Column: '+d);return true;}

 

I ran it only like this :

 

 

<script>'use strict';x = 3.14; function show[]{return x +10 ;} </script>

 

It shew no error

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justsomeguy w3schools Guru

justsomeguy

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is about the logic that drives the code . However , my question was about the syntax and

OK, if you're only asking about the syntax then the parentheses tells it to execute the function.

It shew no error

Well then that's a problem, because putting "[]" after a function name is a syntax error in all versions of Javascript. If you don't see that syntax error then maybe you're not looking in the correct place for error messages.
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hisoka Invested Member

hisoka

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"OK, if you're only asking about the syntax then the parentheses tells it to execute the function."

 

again my question was not what is the role of the parenthesis

 

my question was :

 

Syntactically , why we used init in window.onload = init; and fnd in document.getElementById('btn1').onclick = fnd; without parenthesis ??

 

in other words , why init in :

 

window.onload = init; is used without parenthesis

 

why fnd in document.getElementById('btn1').onclick = fnd is used without parenthesis

 

in other words

 

syntactically , why init in window.onload = init is like this :

 

window.onload = init and not like this window.onload = init() and the same for fnd ??

 

 

"you don't see that syntax error then maybe you're not looking in the correct place for error messages"

what do you mean ?

 

I read the content of the link you gave from the beginning to the end and I did as the page says . However , I forget to say that I have mozilla version 36.0.1 and may be it does not support strict mode

 

 

"Obviously you aren't going to see an error unless you use an onerror codeblock"

 

it is not written in the strict mode tutorial page you gave me that I should use "onerror codeblock" :)

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davej Devoted Member

davej

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You have been talking about using the browser console for weeks now. Have you never seen a Javascript error in the browser console? The onerror codeblock is a non-standard item that I add to my own code but most developers simply use the browser developer console.

 

https://developer.chrome.com/devtools/docs/console

 

https://developer.mozilla.org/en-US/docs/Tools/Browser_Console

 

https://msdn.microsoft.com/en-us/library/dd565625%28v=vs.85%29.aspx

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justsomeguy w3schools Guru

justsomeguy

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in other wordssyntactically , why init in window.onload = init is like this :window.onload = init and not like this window.onload = init() and the same for fnd ??

I've already explained it both syntactically and semantically. Go back and review my answers. If you do not know what effect adding the parentheses has, then look that up also.

I have mozilla version 36.0.1 and may be it does not support strict mode

It does.
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hisoka Invested Member

hisoka

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"I've already explained it both syntactically and semantically. Go back and review my answers. If you do not know what effect adding the parentheses has, then look that up also."

 

this is what you wrote to me :

 

"OK, if you're only asking about the syntax then the parentheses tells it to execute the function."

 

this is the reformulation of your answer : the parentheses tell it (tell this window.onload and thisdocument.getElementById('btn1').onclick ) to execute the function . All what you did in your answer is telling me the role of the parentheses

 

did I ask about the role of the parentheses so that you answer me the parentheses tells it to execute the function??! if I did then please show me where (copy paste)

 

I asked the contrary :

 

first question :

 

Posted 11 March 2015 - 11:21 PM

 

Syntactically , why we used init in window.onload = init; and fnd in document.getElementById('btn1').onclick = fnd; without parenthesis ??

 

same question :

 

Posted Yesterday, 03:07 PM:

 

why init in window.onload = init; is used without parenthesis ?

 

 

 

why fnd in document.getElementById('btn1').onclick = fnd is used without parenthesis ?

 

I was asking why they are used without parentheses and you answered :

then the parentheses tells it to execute the function

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hisoka Invested Member

hisoka

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window.onload = init; is used without parenthesis

 

why fnd in document.getElementById('btn1').onclick = fnd is used without parenthesis

 

In JavaScript , there are what we call event handlers . Event handlers are little codes (methods) used to tell the browser what to do when an event occurs.

 

the syntax of an event handler is like this

 

[element].[event]=[function]

 

element is a property of the document

 

event is the event that will occur like clicking the mouse

 

function is the function that will run once the event occurs.

 

 

Now I will answer this question :

 

window.onload = init; is used without parenthesis

 

why fnd in document.getElementById('btn1').onclick = fnd is used without parenthesis

 

it is simple because init or fnd without parentheses is a reference to a function and not a function . In other word init without parentheses is a reference a pointer to the function init() in

 

function init() {document.getElementById('btn1').onclick = fnd;}

 

and fnd without parentheses is a pointer or a reference to the function fnd() in

 

function fnd(){document.write("writing this text overwrites the entire document");}

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justsomeguy w3schools Guru

justsomeguy

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Good lord. You asked what it means syntactically. When you add the parentheses, it executes the function. So guess what it does when you don't add the parentheses? Do you think it executes the function?I cannot state it any more clearly. So, I'll just paste what I wrote before.

This line:window.onload = init;Tells it to assign the function init to the window.onload handler. This line:window.onload = init();Tells it to execute the function init and assign the return value of that function to the window.onload handler.

That's pretty simple. That is what happens both with and without parentheses. If you're looking for something other than an explanation of what happens if you use parentheses, and also if you don't, then I don't know what you're asking.Here's a tip: if you are asking for free help from volunteers, and you are not getting the answers that you expect, then maybe you're not asking the right questions.
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hisoka Invested Member

hisoka

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your answers are good . Especially yours . They are an inspiration for me and especially yours . Continue like this . Give me all what you know . It is always useful what you wrote .

 

"and you are not getting the answers that you expect"

 

I expect only one thing : To understand what is going on regardless of the answer . All answers are useful . What so ever is my reaction to them . It is and it will be in an instructive and scientific way . If I make an error . Correct me .

 

:) :) :)

Edited by hisoka
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