Javascript：如何持续监控变量值
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/4631896/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Javascript: How do constantly monitor variables value
提问by Connor
How do I constantly check a variables value. For example:
我如何不断检查变量值。例如：
if(variable == 'value'){
dosomething();
}
This would work if I constantly looped it or something, but is there an efficient way of triggering that as soon as the variable is set to that value?
如果我不断循环它或其他东西，这会起作用，但是一旦变量设置为该值，是否有一种有效的方法来触发它？
回答by Mike Samuel
Watches for a property to be assigned a value and runs a function when that occurs.
监视要分配值的属性并在发生时运行函数。
Object.watch() for all browsers?talks about cross-browser ways to do Object.watchon browsers that don't support it natively.
Object.watch() 适用于所有浏览器？谈论跨浏览器Object.watch在本地不支持它的浏览器上的方法。
回答by K2Spam
Object.defineProperty(Object.prototype, 'watch', {
value: function(prop, handler){
var setter = function(val){
return val = handler.call(this, val);
};
Object.defineProperty(this, prop, {
set: setter
});
}
});
How to use:
如何使用：
var obj = {};
obj.watch('prop', function(value){
console.log('wow!',value);
});
obj.prop = 3;
回答by Jacob
As @Pekka commented, you can have a timer constantly poll the variable. A better solution, if it's all your code that's changing the variable, is to not just set the variable directly, but rather have all setters call a function. The function could then set the variable and do any additional processing you need.
正如@Pekka 评论的那样，您可以让计时器不断轮询变量。一个更好的解决方案，如果你的所有代码都在改变变量，那么不仅仅是直接设置变量，而是让所有的 setter 调用一个函数。然后该函数可以设置变量并执行您需要的任何其他处理。
function setValue(value) {
myVariable = value;
notifyWatchers();
}
回答by goat
If you encapsulate your variable so that the value can only be set by calling a function, it gives you the opportunity to check the value.
如果您封装变量以便只能通过调用函数来设置值，那么您就有机会检查该值。
function ValueWatcher(value) {
this.onBeforeSet = function(){}
this.onAfterSet = function(){}
this.setValue = function(newVal) {
this.onBeforeSet(value, newVal)
value = newVal;
this.onAfterSet(newVal)
}
this.getValue = function() {
return value;
}
}
var name = new ValueWatcher("chris");
wacthedName.onBeforeChange = function(currentVal, newVal) {
alert("about to change from" + currentVal + " to " + newVal);
}
name.setValue("Connor");
回答by Chandu
Use setInterval:
使用 setInterval：
var key = ''
setInterval(function(){
if(key == 'value'){
dosomething();
}
}, 1000);
