93 lines
3.6 KiB
Markdown
93 lines
3.6 KiB
Markdown
# Events: change, input, cut, copy, paste
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Let's cover various events that accompany data updates.
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## Event: change
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The `change` event triggers when the element has finished changing.
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For text inputs that means that the event occurs when it loses focus.
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For instance, while we are typing in the text field below -- there's no event. But when we move the focus somewhere else, for instance, click on a button -- there will be a `change` event:
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```html autorun height=40 run
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<input type="text" onchange="alert(this.value)">
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<input type="button" value="Button">
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```
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For other elements: `select`, `input type=checkbox/radio` it triggers right after the selection changes:
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```html autorun height=40 run
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<select onchange="alert(this.value)">
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<option value="">Select something</option>
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<option value="1">Option 1</option>
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<option value="2">Option 2</option>
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<option value="3">Option 3</option>
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</select>
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```
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## Event: input
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The `input` event triggers every time after a value is modified by the user.
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Unlike keyboard events, it triggers on any value change, even those that does not involve keyboard actions: pasting with a mouse or using speech recognition to dictate the text.
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For instance:
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```html autorun height=40 run
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<input type="text" id="input"> oninput: <span id="result"></span>
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<script>
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input.oninput = function() {
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result.innerHTML = input.value;
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};
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</script>
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```
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If we want to handle every modification of an `<input>` then this event is the best choice.
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On the other hand, `input` event doesn't trigger on keyboard input and other actions that do not involve value change, e.g. pressing arrow keys `key:⇦` `key:⇨` while in the input.
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```smart header="Can't prevent anything in `oninput`"
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The `input` event occurs after the value is modified.
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So we can't use `event.preventDefault()` there -- it's just too late, there would be no effect.
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```
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## Events: cut, copy, paste
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These events occur on cutting/copying/pasting a value.
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They belong to [ClipboardEvent](https://www.w3.org/TR/clipboard-apis/#clipboard-event-interfaces) class and provide access to the data that is copied/pasted.
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We also can use `event.preventDefault()` to abort the action, then nothing gets copied/pasted.
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For instance, the code below prevents all such events and shows what we are trying to cut/copy/paste:
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```html autorun height=40 run
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<input type="text" id="input">
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<script>
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input.oncut = input.oncopy = input.onpaste = function(event) {
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alert(event.type + ' - ' + event.clipboardData.getData('text/plain'));
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return false;
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};
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</script>
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```
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Please note, that it's possible to copy/paste not just text, but everything. For instance, we can copy a file in the OS file manager, and paste it.
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There's a list of methods [in the specification](https://www.w3.org/TR/clipboard-apis/#dfn-datatransfer) that can work with different data types including files, read/write to the clipboard.
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But please note that clipboard is a "global" OS-level thing. Most browsers allow read/write access to the clipboard only in the scope of certain user actions for the safety, e.g. in `onclick` event handlers.
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Also it's forbidden to generate "custom" clipboard events with `dispatchEvent` in all browsers except Firefox.
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## Summary
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Data change events:
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| Event | Description | Specials |
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|---------|----------|-------------|
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| `change`| A value was changed. | For text inputs triggers on focus loss. |
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| `input` | For text inputs on every change. | Triggers immediately unlike `change`. |
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| `cut/copy/paste` | Cut/copy/paste actions. | The action can be prevented. The `event.clipboardData` property gives read/write access to the clipboard. |
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