Javascript 变量的值是否已更改
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value of variable has changed or not
提问by Niraj Choubey
how to find whether a value of variable is changed or not in javascript .
如何在 javascript 中查找变量的值是否已更改。
回答by bezmax
Ehm?
嗯？
var testVariable = 10;
var oldVar = testVariable;
...
if (oldVar != testVariable)
alert("testVariable has changed!");
And no, there is no magical "var.hasChanged()" nor "var.modifyDate()" in Javascript unless you code it yourself.
不，Javascript 中没有神奇的“var.hasChanged()”或“var.modifyDate()”，除非您自己编写代码。
回答by meouw
There is a way to watch variables for changes: Object::watch- some code below
有一种方法可以观察变量的变化：Object::watch- 下面的一些代码
/*
For global scope
*/
// won't work if you use the 'var' keyword
x = 10;
window.watch( "x", function( id, oldVal, newVal ){
alert( id+' changed from '+oldVal+' to '+newVal );
// you must return the new value or else the assignment will not work
// you can change the value of newVal if you like
return newVal;
});
x = 20; //alerts: x changed from 10 to 20
/*
For a local scope (better as always)
*/
var myObj = {}
//you can watch properties that don't exist yet
myObj.watch( 'p', function( id, oldVal, newVal ) {
alert( 'the property myObj::'+id+' changed from '+oldVal+' to '+newVal );
});
myObj.p = 'hello'; //alerts: the property myObj::p changed from undefined to hello
myObj.p = 'world'; //alerts: the property myObj::p changed from hello to world
// stop watching
myObj.unwatch('p');
回答by Solomon Ucko
回答by User 1034
If you are a firefox user you can check using firebug. If you are using IE we can put alert statements and check the values of the variables.
如果您是 firefox 用户，则可以使用 firebug 进行检查。如果您使用的是 IE，我们可以放置警报语句并检查变量的值。
回答by deceze
By comparing it to a known state to see if it differs. If you're looking for something like variable.hasChanged, I'm pretty sure that doesn't exist.
通过将其与已知状态进行比较以查看它是否有所不同。如果您正在寻找类似的东西variable.hasChanged，我很确定它不存在。
