如何使 Javascript setTimeout 在函数中返回值
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how to make Javascript setTimeout returns value in a function
提问by Aberel
I have a function that calls some service and returns the response. If the response is FALSE, it waits 1 second to ask the service again (which then probably returns TRUE).
我有一个函数可以调用一些服务并返回响应。如果响应为 FALSE，则等待 1 秒再次询问服务（然后可能返回 TRUE）。
How can I do to call my function "checkService()" once, and get the real value? (the first or second try, decided by the function) I set the RET value inside the function, but the functions always return the first RET, because the setTimeout is asynchronous.
我怎样才能调用我的函数“checkService()”一次，并获得真正的价值？（第一次或第二次尝试，由函数决定）我在函数内部设置了 RET 值，但函数总是返回第一个 RET，因为 setTimeout 是异步的。
In other words, I need some "sleep" trick, or any solution (may be jQuery too).
换句话说，我需要一些“睡眠”技巧或任何解决方案（也可能是 jQuery）。
function checkService() {
//this may return TRUE or FALSE
var RET = someServiceResponse();
// here waits 1 second, then ask the service again
if( RET == true ) {
return true;
} else {
setTimeout(
function() {
//it must return the second response of the service
RET = someServiceResponse();
},
1000
);
// I want the checkService() return the response after de timeout
return RET;
}
}
function alertResponse() {
alert( checkService() );
}
回答by Rapha?l Malié
You should use a callback function when you expect a result from the service.
当您期望服务的结果时，您应该使用回调函数。
Like this :
像这样 ：
function checkService(callback) {
//this may return TRUE or FALSE
var RET = someServiceResponse();
// here waits 1 second, then ask the service again
if( RET == true ) {
callback(RET);
} else {
setTimeout(
function() {
//it must return the second response of the service
RET = someServiceResponse();
callback(RET);
},
1000
);
// I want the checkService() return the response after de timeout
return RET;
}
}
So when you want to call the service, you just need to do :
因此，当您想调用该服务时，您只需要执行以下操作：
checkService(function(status){
alert(status);
// Here some code after the webservice response
});
回答by elzi
Googling 'javascript setTimeout callback' here's a handy jsFiddle about 3 results down:
谷歌搜索“javascript setTimeout 回调”，这是一个方便的 jsFiddle，大约有 3 个结果：
getData('http://fakedomain1234.com/userlist', writeData);
document.getElementById('output').innerHTML += "show this before data ...";
function getData(dataURI, callback) {
// Normally you would actually connect to a server here.
// We're just going to simulate a 3-second delay.
var timer = setTimeout(function () {
var dataArray = [123, 456, 789, 012, 345, 678];
callback(dataArray);
}, 3000);
}
function writeData(myData) {
console.log(myData);
}
