假设 中有一个代码地点 2
var place2IsReady = true;
在 地点 1 我需要实现以下逻辑:Once place2IsReady value was changed (to true) then display alert('ready!');
笔记:解决方案一
我相信我可以改用 window.place2IsReady 并使用 setTimeout/setInterval 代替 1 直到我得到
window.place2IsReady === true
.有更好的选择吗?使用监听器?关于变量的变化?
附言我需要追踪 只有第一个可能的改变 place2IsReady。
有没有更好的办法?谢谢你。
最佳答案
您可以使用 setTimeout
创建变量更改的监听器。 , 就像是:
let place2IsReady = false;
setReadyListener();
// testing wait 2 seconds to set place2IsReady to true
// so: an alert should occur after 2 seconds
setTimeout(() => place2IsReady = true, 2000);
function setReadyListener() {
const readyListener = () => {
if (place2IsReady) {
return alert("Ready!");
}
return setTimeout(readyListener, 250);
};
readyListener();
}
更通用的监听器“工厂”可能是:
let place2IsReady = false;
let fromObj = {
place2IsReady: "busy",
done() { this.place2IsReady = "done"; },
};
const listen = changeListenerFactory();
listen(
() => place2IsReady,
() => console.log("place2IsReady") );
listen(
() => fromObj.place2IsReady === "done",
() => console.log("formObj.place2IsReady done!") );
console.log("Listening...");
// test change variables with listeners
setTimeout(() => place2IsReady = true, 1000);
setTimeout(() => fromObj.done(), 3000);
function changeListenerFactory() {
const readyListener = (condition, callback, delay) => {
if (!condition || typeof condition !== "function") { return true; }
if (condition()) {
return callback();
}
setTimeout(() => readyListener(condition, callback, delay), delay);
};
return (condition, callback = () => {}, delay = 250) =>
readyListener(condition, callback, delay);
}
或者也许使用 Proxy (带有固定陷阱)为您工作
const readyState = new Proxy({ ready: false }, {
set (target, prop, val) {
console.log(`readyState.ready changed from ${target[prop]} to ${val}`);
target[prop] = val;
}
});
console.log("Waiting for changes ...");
setTimeout(() => readyState.ready = true, 2000);
关于javascript - 监听js变量变化,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/65937827/