javascript function wait until another function to

问题:

I have two javascript functions that are called from android. After long debug sessions finally I realized that the problem is arising from the fact that second function is getting called before first one is finished. I already searched the examples with deferred etc, but they all depends on function calls within another one.

function FunctInit(someVarible){ //someVariable is sent from android, cannot call again from getResult
//init and fill screen
}

function getResult(){ //also getResult need to be called from android via button
//return some variables
}

How can I force getResult to wait FuncInit? Is there a way to achieve this via Javascript?

回答1:

In my opinion, deferreds/promises (as you have mentionned) is the way to go, rather than using timeouts.

Here is an example I have just written to demonstrate how you could do it using deferreds/promises.

Take some time to play around with deferreds. Once you really understand them, it becomes very easy to perform asynchronous tasks.

Hope this helps!

$(function(){
    function1().done(function(){
        // function1 is done, we can now call function2
        console.log('function1 is done!');

        function2().done(function(){
            //function2 is done
            console.log('function2 is done!');
        });
    });
});

function function1(){
    var dfrd1 = $.Deferred();
    var dfrd2= $.Deferred();

    setTimeout(function(){
        // doing async stuff
        console.log('task 1 in function1 is done!');
        dfrd1.resolve();
    }, 1000);

    setTimeout(function(){
        // doing more async stuff
        console.log('task 2 in function1 is done!');
        dfrd2.resolve();
    }, 750);

    return $.when(dfrd1, dfrd2).done(function(){
        console.log('both tasks in function1 are done');
        // Both asyncs tasks are done
    }).promise();
}

function function2(){
    var dfrd1 = $.Deferred();
    setTimeout(function(){
        // doing async stuff
        console.log('task 1 in function2 is done!');
        dfrd1.resolve();
    }, 2000);
    return dfrd1.promise();
}

回答2:

There are several ways I can think of to do this.

Use a callback:

 function FunctInit(someVarible){
      //init and fill screen
      AndroidCallGetResult();  // Enables Android button.
 }

 function getResult(){ // Called from Android button only after button is enabled
      //return some variables
 }

Use a Timeout (this would probably be my preference):

 var inited = false;
 function FunctInit(someVarible){
      //init and fill screen
      inited = true;
 }

 function getResult(){
      if (inited) {
           //return some variables
      } else {
           setTimeout(getResult, 250);
      }
 }

Wait for the initialization to occur:

 var inited = false;
 function FunctInit(someVarible){
      //init and fill screen
      inited = true;
 }

 function getResult(){
      var a = 1;
      do { a=1; }
      while(!inited);
      //return some variables
 }

回答3:

Following answer can help in this and other similar situations like synchronous AJAX call -

Working example

waitForMe().then(function(intentsArr){
  console.log('Finally, I can execute!!!');
},
function(err){
  console.log('This is error message.');
})

function waitForMe(){
    // Returns promise
    console.log('Inside waitForMe');
    return new Promise(function(resolve, reject){
        if(true){ // Try changing to 'false'
            setTimeout(function(){
                console.log('waitForMe\'s function succeeded');
                resolve();
            }, 2500);
        }
        else{
            setTimeout(function(){
                console.log('waitForMe\'s else block failed');
                resolve();
            }, 2500);
        }
    });
}