Javascript, by itself, does not have a wait function. However, you can
create a pseudo wait function by doing the following:
while( !input_available() )
mch_delay(50);
.
.
.
function mch_delay( time )
{
if( time !== undefined ){ settimeout( "mch_delay()", time ); }
else return true;
return false;
}
If the above is called with a time it will set the timeout and then
return false. This might seem like it will cause the program to do
nothing else but the timeout retains its own return information about
where it came from. Basically, javascript splits (or does a fork) on
the timeout. So the next thing it will do is to hit the "return
false". The return false will be the flag to say "stop this branch of
the process". When the timeout kicks back in though, it will be calling
the function without a time on the call line. This will make the ELSE
branch fire off which will return true and your program will continue.
The thing to note is - you have to take the false return into
consideration. The problem with Javascript is two fold: 1)No sleep
function, and 2)No END/EXIT function either. In looking for a way to
exit a program I found this:
|function exit( status) {
// http://kevin.vanzonneveld.net
// + original by: Brett Zamir (http://brettz9.blogspot.com)
// + input by: Paul
// + bugfixed by: Hyam Singer (http://www.impact-computing.com/)
// + improved by: Philip Peterson
// + bugfixed by: Brett Zamir (http://brettz9.blogspot.com)
// % note 1: Should be considered experimental. Please comment on
this function.
// * example 1: exit();
// * returns 1: null
var i;
if (typeof status=== 'string') {
alert(status);
}
window.addEventListener('error', function (e)
{e.preventDefault();e.stopPropagation();}, false);
var handlers= [
'copy', 'cut', 'paste',
'beforeunload', 'blur', 'change', 'click', 'contextmenu',
'dblclick', 'focus', 'keydown', 'keypress', 'keyup', 'mousedown',
'mousemove', 'mouseout', 'mouseover', 'mouseup', 'resize', 'scroll',
'DOMNodeInserted', 'DOMNodeRemoved', 'DOMNodeRemovedFromDocument',
'DOMNodeInsertedIntoDocument', 'DOMAttrModified', 'DOMCharacterDataModified',
'DOMElementNameChanged', 'DOMAttributeNameChanged', 'DOMActivate',
'DOMFocusIn', 'DOMFocusOut', 'online', 'offline', 'textInput',
'abort', 'close', 'dragdrop', 'load', 'paint', 'reset', 'select',
'submit', 'unload'
];
function stopPropagation(e) {
e.stopPropagation();
// e.preventDefault(); // Stop for the form controls, etc., too?
}
for (i=0; i< handlers.length; i++) {
window.addEventListener(handlers[i], function (e)
{stopPropagation(e);}, true);
}
if (window.stop) {
window.stop();
}
throw '';
}
So the "return false" could be changed to using the above - if it works.
Otherwise, just check for the false value
being returned and act accordingly.
I hope this helps. :-)
|
On 11/29/2013 11:29 PM, ?? wrote:
Hi all,
I'm now trying to port vim into javascript with emscripten.
The main barrier I found is that the async model of JavaScript. JavaScript
is event-driven, and there is no mechanism to sleep and wait for events to be
processed, so the following won't work:
```
void wait_for_input()
{
// wait until there's some input
while(!input_available())
mch_delay(50); // there's no sleep() in JavaScript, and we cannot do a
busy-wait here
}
// in gui_start()
// do something
wait_for_input()
// do something else
```
Instead we have to split the function to make the function call async:
```
static callback_t wait_for_input_cb;
void wait_for_input()
{
if(!input_available())
mch_delay_async(50, wait_for_input);
else
wait_for_input_cb();
}
// in gui_start()
// do something
wait_for_input_cb = gui_start_cb;
wait_for_input();
} // end gui_start() here
void gui_start_cb()
{
// do something else
```
Generally it's hard to maintain both versions, I'm trying to define some
macros to ease the process, but the code is still not readable due to function
splitting. The easiest way of doing this is to simulate the async model in the
sync model, which would however introduce (un-necessary) overhead for sync
situations.
The worst case is that the async (JavaScript) version has to be maintained
separately, but I wonder if there are better solutions?
Please let me know what you guys think about it.
Thanks!
regards,
- Lu Wang
2013.11.30
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