jeena/en.javascript.info
1
0
Fork 0
Code Issues Pull requests Projects Packages Wiki Activity Actions

changes

Browse source
This commit is contained in:
Ilya Kantor 2017-03-23 11:06:57 +03:00
parent b6ed18e70d
commit c9401b3104
15 changed files with 231 additions and 233 deletions
Download patch file Download diff file Expand all files Collapse all files

89
2-ui/3-event-details/1-mouse-events-basics/article.md
View file

@ -1,6 +1,6 @@
# Mouse events basics
In this chapter we'll get into more details of mouse events and their properties.
In this chapter we'll get into more details about mouse events and their properties.
[cut]
@ -16,12 +16,12 @@ The most used simple events are:
: Mouse button is clicked/released over an element.
`mouseover/mouseout`
: Mouse pointer comes over/out an element.
: Mouse pointer comes over/out from an element.
`mousemove`
: Every mouse move over an element triggers that event.
There are several other event types too, we'll cover them later.
...There are several other event types too, we'll cover them later.
### Complex events
@ -36,7 +36,7 @@ There are several other event types too, we'll cover them later.
Complex events are made of simple ones, so in theory we could live without them. But they exist, and that's good, because they are convenient.
For touchscreen devices mouse events also happen, because they are emulated.
For touchscreen and touchpad devices mouse events also happen, they are emulated.
### Events order
@ -44,25 +44,25 @@ An action may trigger multiple events.
For instance, a click first triggers `mousedown`, when the button is pressed, then `mouseup` and `click` when it's released.
In cases when a single action initiated multiple events, their order is fixed. That is, the handlers are be called in the order `mousedown` -> `mouseup` -> `click`. Events are handled in sequence: `onmouseup` finishes before `onclick` runs.
In cases when a single action initiates multiple events, their order is fixed. That is, the handlers are called in the order `mousedown` -> `mouseup` -> `click`. Events are handled in the same sequence: `onmouseup` finishes before `onclick` runs.
```online
Click the button below and you'll see which events happen. Try double-click too.
Click the button below and you'll see the events. Try double-click too.
On the teststand below all mouse events are logged, and if there are more than 1 second delay between them, then they are separated by a horizontal ruler.
Also we can see the `which` property that allows to detect the mouse button. We'll cover it a bit later.
Also we can see the `which` property that allows to detect the mouse button.
<input onmousedown="return logMouse(event)" onmouseup="return logMouse(event)" onclick="return logMouse(event)" oncontextmenu="return logMouse(event)" ondblclick="return logMouse(event)" value="Click me with the right or the left mouse button" type="button"> <input onclick="logClear('test')" value="Clear" type="button"> <form id="testform" name="testform"> <textarea style="font-size:12px;height:150px;width:360px;"></textarea></form>
```
## Getting the button: which
Click-related events always have the `which` property that allows to see the button.
Click-related events always have the `which` property that allows to get the button.
It is not used for `click` and `contextmenu` events, because the former happens only on left-click, and the latter -- only on right-click.
But if we track `mousedown` and `mouseup`, then we need it, because they trigger on any button.
But if we track `mousedown` and `mouseup`, then we need it, because these events trigger on any button, so `which` allows to distinguish between "right-mousedown" and "left-mousedown".
There are the three possible values:
@ -70,7 +70,7 @@ There are the three possible values:
- `event.which == 2` - the middle button
- `event.which == 3` - the right button
The middle button is somewhat exotic right now.
The middle button is somewhat exotic right now and is very rarely used.
## Modifiers: shift, alt, ctrl and meta
@ -81,7 +81,7 @@ The properties are:
- `shiftKey`
- `altKey`
- `ctrlKey`
- `metaKey` (for Mac)
- `metaKey` (`key:Cmd` for Mac)
For instance, the button below only works on `key:Alt+Shift`+click:
@ -100,13 +100,13 @@ For instance, the button below only works on `key:Alt+Shift`+click:
```
```warn header="Attention: on Mac it's usually `Cmd` instead of `Ctrl`"
On Windows and Linux there are modifier keys `key:Alt`, `key:Shift` and `key:Ctrl`. On Mac there's one more: `key:Cmd`, that corresponds to the property `metaKey`.
On Windows and Linux there are modifier keys `key:Alt`, `key:Shift` and `key:Ctrl`. On Mac there's one more: `key:Cmd`, it corresponds to the property `metaKey`.
In most cases when Windows/Linux uses `key:Ctrl`, on Mac people use `key:Cmd`. So where a Windows user presses `key:Ctrl+Enter` or `key:Ctrl+A`, a Mac user would press `key:Cmd+Enter` or `key:Cmd+A`, and so on, most apps use `key:Cmd` instead of `key:Ctrl`.
So if we want to support combinations like `key:Ctrl`+click, then for Mac it makes sense to use `key:Cmd`+click. That's more comfortable for Mac users.
Even if we'd like to force Mac users to `key:Ctrl`+click -- that's kind of difficult. The problem is: a regular click with `key:Ctrl` is interpreted as a *right click* on Mac, and it generates the `contextmenu` event, not `click` like Windows/Linux.
Even if we'd like to force Mac users to `key:Ctrl`+click -- that's kind of difficult. The problem is: a left-click with `key:Ctrl` is interpreted as a *right-click* on Mac, and it generates the `contextmenu` event, not `click` like Windows/Linux.
So if we want users of all operational systems to feel comfortable, then together with `ctrlKey` we should use `metaKey`.
@ -114,7 +114,8 @@ For JS-code it means that we should check `if (event.ctrlKey || event.metaKey)`.
```
```warn header="There are also mobile devices"
Keyboard combinations are good as an addition to the workflow. So that if you have keyboard -- it works. And if your device doesn't have it -- then there's another way to do the same.
Keyboard combinations are good as an addition to the workflow. So that if the visitor has a
keyboard -- it works. And if your device doesn't have it -- then there's another way to do the same.
```
## Coordinates: clientX/Y, pageX/Y
@ -124,37 +125,24 @@ All mouse events have coordinates in two flavours:
1. Window-relative: `clientX` and `clientY`.
2. Document-relative: `pageX` and `pageY`.
See more about coordinates the chapter <info:coordinates>.
For instance, if we have a window of the size 500x500, and the mouse is in the center, then `clientX` and `clientY` are `250`.
If we scroll the page, but the mouse is still in the center, then `clientX/Y` don't change, because they are window-relative.
For instance, if we have a window of the size 500x500, and the mouse is in the left-upper corner, then `clientX` and `clientY` are `0`. And if the mouse is in the center, then `clientX` and `clientY` are `250`, no matter what place in the document it is. They are similar to `position:fixed`.
````online
Move the mouse over the input field to see `clientX/clientY`:
Move the mouse over the input field to see `clientX/clientY` (it's in the `iframe`, so coordinates are relative to that `iframe`):
```html autorun height=50
<input onmousemove="this.value = event.clientX+':'+event.clientY">
<input onmousemove="this.value=event.clientX+':'+event.clientY" value="Mouse over me">
```
````
That's like `elem.getBoundingClientRect()` and `position:fixed`.
Document-relative coordinates are counted from the left-upper corner of the document, not the window.
Coordinates `pageX`, `pageY` are similar to `position:absolute` on the document level.
Document-relative coordinates are counted from the left-upper corner of the document, not the window. In case of a scrolled page, they also include the scrolled out left-upper part.
These coordinates are connected by the formulas:
```js
// for an arbitrary mouse event
event.pageX = pageXOffset + event.clientX
event.pageY = pageYOffset + event.clientY
```
So technically we don't need `pageX/Y`, because we can always calculate them using the formulas. But it's good that we have them, as a matter of convenience.
You can read more about coordinates in the chapter <info:coordinates>.
## No selection on mousedown
Mouse clicks have a side-effect that may be disturbing. A double click or an occasional cursor move with a pressed button select the text.
Mouse clicks have a side-effect that may be disturbing. A double click selects the text.
If we want to handle click events ourselves, then the "extra" selection doesn't look good.
@ -166,7 +154,7 @@ For instance, a double-click on the text below selects it in addition to our han
There's a CSS way to stop the selection: the `user-select` property from [CSS UI Draft](https://www.w3.org/TR/css-ui-4/).
It's yet in the draft, so browser support it with prefixes:
Most browsers support it with prefixes:
```html autorun height=50
<style>
@ -185,15 +173,15 @@ Before...
...After
```
Now if you double-click on `"Unselectable"`, it doesn't get selected. Seems to work.
Now if you double-click on "Unselectable", it doesn't get selected. Seems to work.
...But there is a side-effect! The text became truly unselectable. Even if a user starts the selection from `"Before"` and ends with `"After"`, the selection skips `"Unselectable"` part. Do we really want to make our text unselectable?
...But there is a potential problem! The text became truly unselectable. Even if a user starts the selection from "Before" and ends with "After", the selection skips "Unselectable" part. Do we really want to make our text unselectable?
Most of time, not really. A user may want to select it, for copying or other needs. That may be disturbing if we don't allow him to do it. So the solution is not that good.
Most of time, we don't. A user may have valid reasons to select the text, for copying or other needs. That may be disturbing if we don't allow him to do it. So the solution is not that good.
What we want is to "fix" our interface. We don't want the selection to occur on double-click, that's it.
What we want is to prevent the selection on double-click, that's it.
An alternative solution would be to handle `mousedown`, like this:
A text selection is the default browser action on `mousedown` event. So the alternative solution would be to handle `mousedown` and prevent it, like this:
```html autorun height=50
Before...
@ -203,9 +191,9 @@ Before...
...After
```
The selection is started on `mousedown` as a default browser action. So if we prevent it, then the bold element is not selected any more on clicks. That's as intended.
Now the bold element is not selected on double clicks.
From the other hand, the text inside it is still selectable. The only limitation: the selection should start not on the text itself, but from "before" or "after" it. Usually that's not a problem.
From the other hand, the text inside it is still selectable. The selection should start not on the text itself, but before or after it. Usually that's fine.
````smart header="Canceling the selection"
Instead of *preventing* the selection, we can cancel it "post-factum" in the event handler.
@ -220,7 +208,7 @@ Before...
...After
```
If you double-click on the bold element, then the selection appears and then is immediately removed. That doesn't look nice, and is not fully reliable though.
If you double-click on the bold element, then the selection appears and then is immediately removed. That doesn't look nice though.
````
````smart header="Preventing copying"
@ -230,31 +218,28 @@ If we want to disable selection to protect our content from copy-pasting, then w
<div *!*oncopy="alert('Copying forbidden!');return false"*/!*>
Dear user,
The copying is forbidden for you.
If you know JS or HTML, then that's not a problem of course,
otherwise we're sorry.
If you know JS or HTML, then you can get everything from the page source though.
</div>
```
If you try to copy a piece of text in the `<div>`, that won't work, because the default action `oncopy` is prevented.
Surely that doesn't stop from opening HTML-source and doing things manually, but not everyone knows how to do it.
Surely that can't stop the user from opening HTML-source, but not everyone knows how to do it.
````
## Summary
Mouse events have following properties:
- Button: `which`
- Button: `which`.
- Modifier keys (`true` if pressed): `altKey`, `ctrlKey`, `shiftKey` and `metaKey` (Mac).
- If you want to handle `key:Ctrl`, then don't forget Mac users, they use `key:Cmd`, so it's better to check `if (e.metaKey || e.ctrlKey)`.
- Window-relative coordinates: `clientX/clientY`
- Document-relative coordinates: `pageX/clientX`
- Window-relative coordinates: `clientX/clientY`.
- Document-relative coordinates: `pageX/clientX`.
In the tasks below it's also important to deal with the selection as an unwanted side-effect of clicks.
There are several ways, for instance:
1. CSS-property `user-select:none` (with browser prefixes) completely disables it.
2. Cancel the selection post-factum using `getSelection().removeAllRanges()`.
3. Handle `mousedown` and prevent the default action.
The third way is preferred most of the time.
3. Handle `mousedown` and prevent the default action (usually the best).