Call a function after previous function is complete
JavascriptJqueryJavascript Problem Overview
I have the following JavaScript code:
$('a.button').click(function(){
if (condition == 'true'){
function1(someVariable);
function2(someOtherVariable);
}
else {
doThis(someVariable);
}
});
How can I ensure that function2
is called only after function1
has completed?
Javascript Solutions
Solution 1 - Javascript
Specify an anonymous callback, and make function1 accept it:
$('a.button').click(function(){
if (condition == 'true'){
function1(someVariable, function() {
function2(someOtherVariable);
});
}
else {
doThis(someVariable);
}
});
function function1(param, callback) {
...do stuff
callback();
}
Solution 2 - Javascript
If you're using jQuery 1.5 you can use the new Deferreds pattern:
$('a.button').click(function(){
if(condition == 'true'){
$.when(function1()).then(function2());
}
else {
doThis(someVariable);
}
});
Edit: Updated blog link:
Rebecca Murphy had a great write-up on this here: http://rmurphey.com/blog/2010/12/25/deferreds-coming-to-jquery/
Solution 3 - Javascript
Try this :
function method1(){
// some code
}
function method2(){
// some code
}
$.ajax({
url:method1(),
success:function(){
method2();
}
})
Solution 4 - Javascript
promises
, a JavaScript feature of the ECMAScript 6
standard. If your target platform does not support promises
, polyfill it with PromiseJs.
This answer uses Promises are a new (and a lot better) way to handle asynchronous operations in JavaScript:
$('a.button').click(function(){
if (condition == 'true'){
function1(someVariable).then(function() {
//this function is executed after function1
function2(someOtherVariable);
});
}
else {
doThis(someVariable);
}
});
function function1(param, callback) {
return new Promise(function (fulfill, reject){
//do stuff
fulfill(result); //if the action succeeded
reject(error); //if the action did not succeed
});
}
This may seem like a significant overhead for this simple example, but for more complex code it is far better than using callbacks. You can easily chain multiple asynchronous calls using multiple then
statements:
function1(someVariable).then(function() {
function2(someOtherVariable);
}).then(function() {
function3();
});
You can also wrap jQuery deferrds easily (which are returned from $.ajax
calls):
Promise.resolve($.ajax(...params...)).then(function(result) {
//whatever you want to do after the request
});
As @charlietfl noted, the jqXHR
object returned by $.ajax()
implements the Promise
interface. So it is not actually necessary to wrap it in a Promise
, it can be used directly:
$.ajax(...params...).then(function(result) {
//whatever you want to do after the request
});
Solution 5 - Javascript
Or you can trigger a custom event when one function completes, then bind it to the document:
function a() {
// first function code here
$(document).trigger('function_a_complete');
}
function b() {
// second function code here
}
$(document).bind('function_a_complete', b);
Using this method, function 'b' can only execute AFTER function 'a', as the trigger only exists when function a is finished executing.
Solution 6 - Javascript
you can do it like this
$.when(funtion1()).then(function(){
funtion2();
})
Solution 7 - Javascript
This depends on what function1 is doing.
If function1 is doing some simple synchrounous javascript, like updating a div value or something, then function2 will fire after function1 has completed.
If function1 is making an asynchronous call, such as an AJAX call, you will need to create a "callback" method (most ajax API's have a callback function parameter). Then call function2 in the callback. eg:
function1()
{
new AjaxCall(ajaxOptions, MyCallback);
}
function MyCallback(result)
{
function2(result);
}
Solution 8 - Javascript
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>
Solution 9 - Javascript
If function1 is some sync function that you want to turn into an async one because it takes some time to complete, and you have no control over it to add a callback :
function function1 (someVariable) {
var date = Date.now ();
while (Date.now () - date < 2000); // function1 takes some time to complete
console.log (someVariable);
}
function function2 (someVariable) {
console.log (someVariable);
}
function onClick () {
window.setTimeout (() => { function1 ("This is function1"); }, 0);
window.setTimeout (() => { function2 ("This is function2"); }, 0);
console.log ("Click handled"); // To show that the function will return before both functions are executed
}
onClick ();
The output will be :
Click handled
...and after 2 seconds :
This is function 1
This is function 2
This works because calling window.setTimeout () will add a task to the JS runtine task loop, which is what an async call makes, and because the basic principle of "run-to-completion" of the JS runtime ensures that onClick () is never interrupted before it ends.
Notice that this as funny as it makes the code difficult to understand...