How should I call 3 functions in order to execute them one after the other?
If I need call this functions one after other,
$('#art1').animate({'width':'1000px'},1000);
$('#art2').animate({'width':'1000px'},1000);
$('#art3').animate({'width':'1000px开发者_Python百科'},1000);
I know in jQuery I could do something like:
$('#art1').animate({'width':'1000px'},1000,'linear',function(){
$('#art2').animate({'width':'1000px'},1000,'linear',function(){
$('#art3').animate({'width':'1000px'},1000);
});
});
But, let's assume that I'm not using jQuery and I want to call:
some_3secs_function(some_value);
some_5secs_function(some_value);
some_8secs_function(some_value);
How I should call this functions in order to execute some_3secs_function, and AFTER that call ends, then execute some_5secs_function and AFTER that call ends, then call some_8secs_function?
UPDATE:
This still not working:
(function(callback){
$('#art1').animate({'width':'1000px'},1000);
callback();
})((function(callback2){
$('#art2').animate({'width':'1000px'},1000);
callback2();
})(function(){
$('#art3').animate({'width':'1000px'},1000);
}));
Three animations start at same time
Where is my mistake?
In Javascript, there are synchronous and asynchronous functions.
Synchronous Functions
Most functions in Javascript are synchronous. If you were to call several synchronous functions in a row
doSomething();
doSomethingElse();
doSomethingUsefulThisTime();
they will execute in order. doSomethingElse will not start until doSomething has completed. doSomethingUsefulThisTime, in turn, will not start until doSomethingElse has completed.
Asynchronous Functions
Asynchronous function, however, will not wait for each other. Let us look at the same code sample we had above, this time assuming that the functions are asynchronous
doSomething();
doSomethingElse();
doSomethingUsefulThisTime();
The functions will be initialized in order, but they will all execute roughly at the same time. You can't consistently predict which one will finish first: the one that happens to take the shortest amount of time to execute will finish first.
But sometimes, you want functions that are asynchronous to execute in order, and sometimes you want functions that are synchronous to execute asynchronously. Fortunately, this is possible with callbacks and timeouts, respectively.
Callbacks
Let's assume that we have three asynchronous functions that we want to execute in order, some_3secs_function, some_5secs_function, and some_8secs_function.
Since functions can be passed as arguments in Javascript, you can pass a function as a callback to execute after the function has completed.
If we create the functions like this
function some_3secs_function(value, callback){
//do stuff
callback();
}
then you can call then in order, like this:
some_3secs_function(some_value, function() {
some_5secs_function(other_value, function() {
some_8secs_function(third_value, function() {
//All three functions have completed, in order.
});
});
});
Timeouts
In Javascript, you can tell a function to execute after a certain timeout (in milliseconds). This can, in effect, make synchronous functions behave asynchronously.
If we have three synchronous functions, we can execute them asynchronously using the setTimeout function.
setTimeout(doSomething, 10);
setTimeout(doSomethingElse, 10);
setTimeout(doSomethingUsefulThisTime, 10);
This is, however, a bit ugly and violates the DRY principle[wikipedia]. We could clean this up a bit by creating a function that accepts an array of functions and a timeout.
function executeAsynchronously(functions, timeout) {
for(var i = 0; i < functions.length; i++) {
setTimeout(functions[i], timeout);
}
}
This can be called like so:
executeAsynchronously(
[doSomething, doSomethingElse, doSomethingUsefulThisTime], 10);
In summary, if you have asynchronous functions that you want to execute syncronously, use callbacks, and if you have synchronous functions that you want to execute asynchronously, use timeouts.
This answer uses promises, a JavaScript feature of the ECMAScript 6 standard. If your target platform does not support promises, polyfill it with PromiseJs.
Look at my answer here Wait till a Function with animations is finished until running another Function if you want to use jQuery animations.
Here is what your code would look like with ES6 Promises and jQuery animations.
Promise.resolve($('#art1').animate({ 'width': '1000px' }, 1000).promise()).then(function(){
return Promise.resolve($('#art2').animate({ 'width': '1000px' }, 1000).promise());
}).then(function(){
return Promise.resolve($('#art3').animate({ 'width': '1000px' }, 1000).promise());
});
Normal methods can also be wrapped in Promises.
new Promise(function(fulfill, reject){
//do something for 5 seconds
fulfill(result);
}).then(function(result){
return new Promise(function(fulfill, reject){
//do something for 5 seconds
fulfill(result);
});
}).then(function(result){
return new Promise(function(fulfill, reject){
//do something for 8 seconds
fulfill(result);
});
}).then(function(result){
//do something with the result
});
The then method is executed as soon as the Promise finished. Normally, the return value of the function passed to then is passed to the next one as result.
But if a Promise is returned, the next then function waits until the Promise finished executing and receives the results of it (the value that is passed to fulfill).
It sounds like you're not fully appreciating the difference between synchronous and asynchronous function execution.
The code you provided in your update immediately executes each of your callback functions, which in turn immediately start an animation. The animations, however, execute asyncronously. It works like this:
- Perform a step in the animation
- Call
setTimeoutwith a function containing the next animation step and a delay - Some time passes
- The callback given to
setTimeoutexecutes - Go back to step 1
This continues until the last step in the animation completes. In the meantime, your synchronous functions have long ago completed. In other words, your call to the animate function doesn't really take 3 seconds. The effect is simulated with delays and callbacks.
What you need is a queue. Internally, jQuery queues the animations, only executing your callback once its corresponding animation completes. If your callback then starts another animation, the effect is that they are executed in sequence.
In the simplest case this is equivalent to the following:
window.setTimeout(function() {
alert("!");
// set another timeout once the first completes
window.setTimeout(function() {
alert("!!");
}, 1000);
}, 3000); // longer, but first
Here's a general asynchronous looping function. It will call the given functions in order, waiting for the specified number of seconds between each.
function loop() {
var args = arguments;
if (args.length <= 0)
return;
(function chain(i) {
if (i >= args.length || typeof args[i] !== 'function')
return;
window.setTimeout(function() {
args[i]();
chain(i + 1);
}, 2000);
})(0);
}
Usage:
loop(
function() { alert("sam"); },
function() { alert("sue"); });
You could obviously modify this to take configurable wait times or to immediately execute the first function or to stop executing when a function in the chain returns false or to apply the functions in a specified context or whatever else you might need.
I believe the async library will provide you a very elegant way to do this. While promises and callbacks can get a little hard to juggle with, async can give neat patterns to streamline your thought process. To run functions in serial, you would need to put them in an async waterfall. In async lingo, every function is called a task that takes some arguments and a callback; which is the next function in the sequence. The basic structure would look something like:
async.waterfall([
// A list of functions
function(callback){
// Function no. 1 in sequence
callback(null, arg);
},
function(arg, callback){
// Function no. 2 in sequence
callback(null);
}
],
function(err, results){
// Optional final callback will get results for all prior functions
});
I've just tried to briefly explain the structure here. Read through the waterfall guide for more information, it's pretty well written.
your functions should take a callback function, that gets called when it finishes.
function fone(callback){
...do something...
callback.apply(this,[]);
}
function ftwo(callback){
...do something...
callback.apply(this,[]);
}
then usage would be like:
fone(function(){
ftwo(function(){
..ftwo done...
})
});
Since you tagged it with javascript, I would go with a timer control since your function names are 3, 5, and 8 seconds. So start your timer, 3 seconds in, call the first, 5 seconds in call the second, 8 seconds in call the third, then when it's done, stop the timer.
Normally in Javascript what you have is correct for the functions are running one after another, but since it looks like you're trying to do timed animation, a timer would be your best bet.
asec=1000;
setTimeout('some_3secs_function("somevalue")',asec*3);
setTimeout('some_5secs_function("somevalue")',asec*5);
setTimeout('some_8secs_function("somevalue")',asec*8);
I won't go into a deep discussion of setTimeout here, but:
- in this case I've added the code to execute as a string. this is the simplest way to pass a var into your setTimeout-ed function, but purists will complain.
- you can also pass a function name without quotes, but no variable can be passed.
- your code does not wait for setTimeout to trigger.
- This one can be hard to get your head around at first: because of the previous point, if you pass a variable from your calling function, that variable will not exist anymore by the time the timeout triggers - the calling function will have executed and it's vars gone.
- I have been known to use anonymous functions to get around all this, but there could well be a better way,
You could also use promises in this way:
some_3secs_function(this.some_value).then(function(){
some_5secs_function(this.some_other_value).then(function(){
some_8secs_function(this.some_other_other_value);
});
});
You would have to make some_value global in order to access it from inside the .then
Alternatively, from the outer function you could return the value the inner function would use, like so:
one(some_value).then(function(return_of_one){
two(return_of_one).then(function(return_of_two){
three(return_of_two);
});
});
ES6 Update
Since async/await is widely available now, this is the way to accomplish the same:
async function run(){
await $('#art1').animate({'width':'1000px'},1000,'linear').promise()
await $('#art2').animate({'width':'1000px'},1000,'linear').promise()
await $('#art3').animate({'width':'1000px'},1000,'linear').promise()
}
Which is basically "promisifying" your functions (if they're not already asynchronous), and then awaiting them
//sample01
(function(_){_[0]()})([
function(){$('#art1').animate({'width':'10px'},100,this[1].bind(this))},
function(){$('#art2').animate({'width':'10px'},100,this[2].bind(this))},
function(){$('#art3').animate({'width':'10px'},100)},
])
//sample02
(function(_){_.next=function(){_[++_.i].apply(_,arguments)},_[_.i=0]()})([
function(){$('#art1').animate({'width':'10px'},100,this.next)},
function(){$('#art2').animate({'width':'10px'},100,this.next)},
function(){$('#art3').animate({'width':'10px'},100)},
]);
//sample03
(function(_){_.next=function(){return _[++_.i].bind(_)},_[_.i=0]()})([
function(){$('#art1').animate({'width':'10px'},100,this.next())},
function(){$('#art2').animate({'width':'10px'},100,this.next())},
function(){$('#art3').animate({'width':'10px'},100)},
]);I use a 'waitUntil' function based on javascript's setTimeout
/*
funcCond : function to call to check whether a condition is true
readyAction : function to call when the condition was true
checkInterval : interval to poll <optional>
timeout : timeout until the setTimeout should stop polling (not 100% accurate. It was accurate enough for my code, but if you need exact milliseconds, please refrain from using Date <optional>
timeoutfunc : function to call on timeout <optional>
*/
function waitUntil(funcCond, readyAction, checkInterval, timeout, timeoutfunc) {
if (checkInterval == null) {
checkInterval = 100; // checkinterval of 100ms by default
}
var start = +new Date(); // use the + to convert it to a number immediatly
if (timeout == null) {
timeout = Number.POSITIVE_INFINITY; // no timeout by default
}
var checkFunc = function() {
var end = +new Date(); // rough timeout estimations by default
if (end-start > timeout) {
if (timeoutfunc){ // if timeout function was defined
timeoutfunc(); // call timeout function
}
} else {
if(funcCond()) { // if condition was met
readyAction(); // perform ready action function
} else {
setTimeout(checkFunc, checkInterval); // else re-iterate
}
}
};
checkFunc(); // start check function initially
};
This would work perfectly if your functions set a certain condition to true, which you would be able to poll. Plus it comes with timeouts, which offers you alternatives in case your function failed to do something (even within time-range. Think about user feedback!)
eg
doSomething();
waitUntil(function() { return doSomething_value===1;}, doSomethingElse);
waitUntil(function() { return doSomethingElse_value===1;}, doSomethingUseful);
Notes
Date causes rough timeout estimates. For greater precision, switch to functions such as console.time(). Do take note that Date offers greater cross-browser and legacy support. If you don't need exact millisecond measurements; don't bother, or, alternatively, wrap it, and offer console.time() when the browser supports it
If method 1 has to be executed after method 2, 3, 4. The following code snippet can be the solution for this using Deferred object in JavaScript.
function method1(){
var dfd = new $.Deferred();
setTimeout(function(){
console.log("Inside Method - 1");
method2(dfd);
}, 5000);
return dfd.promise();
}
function method2(dfd){
setTimeout(function(){
console.log("Inside Method - 2");
method3(dfd);
}, 3000);
}
function method3(dfd){
setTimeout(function(){
console.log("Inside Method - 3");
dfd.resolve();
}, 3000);
}
function method4(){
console.log("Inside Method - 4");
}
var call = method1();
$.when(call).then(function(cb){
method4();
});<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
加载中,请稍侯......
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