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Event.preventDefault()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2015年7月.
概要
如果事件可以被取消，就取消事件（即取消事件的預設行為）。但不會影響事件的傳遞，事件仍會繼續傳遞。
語法
event.preventDefault();範例
Toggling a checkbox is the default action of clicking on a checkbox. This example demonstrates how to prevent that from happening:
<!doctype html><html> <head> <title>preventDefault example</title> </head> <body> <p>Please click on the checkbox control.</p> <form> <label for="id-checkbox">Checkbox</label> <input type="checkbox" /> </form> <script> document.querySelector("#id-checkbox").addEventListener( "click", function (event) { alert("preventDefault will stop you from checking this checkbox!"); event.preventDefault(); }, false, ); </script> </body></html>You can seepreventDefault in actionhere.
The following example demonstrates how invalid text input can be stopped from reaching the input field with preventDefault().
<!DOCTYPE html><html><head><title>preventDefault example</title><script>function Init() { var myTextbox = document.getElementById("my-textbox"); myTextbox.addEventListener("keypress", checkName, false);}function checkName(evt) { var charCode = evt.charCode; if (charCode != 0) { if (charCode < 97 || charCode > 122) { evt.preventDefault(); alert( "Please use lowercase letters only." + "\n" + "charCode: " + charCode + "\n", ); } }}</script></head><body onload="Init ()"> <p>Please enter your name using lowercase letters only.</p> <form> <input type="text" /> </form></body></html>Here is the result of the preceding code:
備註
CallingpreventDefault during any stage of event flow cancels the event, meaning that any default action normally taken by the implementation as a result of the event will not occur.
備註：As of Gecko 6.0, callingpreventDefault() causes theevent.defaultPrevented property's value to becometrue.
你可以查看Event.cancelable 屬性來檢查事件是否能夠被取消。對一個不能被取消的事件呼叫preventDefault() 方法是沒有任何效果的。
preventDefault() 方法不會停止事件傳遞。若要停止事件繼續傳遞，可以使用Event.stopPropagation() 方法。
規範
| Specification |
|---|
| DOM # ref-for-dom-event-preventdefault③ |