Javascript: Synchronous wait/delay method

Question

I have a method that performs an asynchronous ajax request to get some permission information from the server (SharePoint) to beeing cached via JS so that I can access it for CSR. Sometimes this takes a little longer (500ms)... not always, but sometimes the rest of the script is loaded so fast, that it needs the permission before the ajax request ist completed entirely.

Is there a simple method to just delay the output of the method? I tried different stuff with SetTimeout() but notthing worked out.

Here is the simplyfied code...

var Permissions = {
    get: function(key) {
        while (this.cacheLoaded != true) {
            wait(100); //<-- This is what I need
        }
        return (typeof this[key] != 'undefined' && this[key] == true) ? true : false;       
    },
    cacheLoaded: false,
    buildCache: function () {
        // load permissions asynchronously by ajax
        .
        .
        .
        Permissions.cacheLoaded = true;
    }
}
Permissions.buildCache();
.
.
.
doLotsOfOtherStuff();
.
.
.    
//Here is the actual call of the get-function:
if (Permission.get('ALOW_DELETE')) {
    deleteSomething();
}

Of course I could switch the Ajax requst to be synchronous. But this would delay the whole script loading. So actually I want to delay jsut the getter for a couple of milliseconds until the request is finished.

You don't have to make the request synchronous, but you really can't reliably do anything else until the initial request completes anyway. All of the `doLotsOfOtherStuff` etc. has to be done after the cache is loaded -- in the ajax callback. — Explosion Pills, Oct 29 '15 at 22:51
You can't `wait` [just yet](https://jakearchibald.com/2014/es7-async-functions/) - you need to put the logic that needs data inside a callback (or Promise handler) for the AJAX request. — joews, Oct 29 '15 at 22:53
Have you seen [this](http://stackoverflow.com/questions/3709597/wait-until-all-jquery-ajax-requests-are-done)? — Shawn Mehan, Oct 29 '15 at 22:54

score 0 · Answer 1 · answered Oct 31 '15 at 20:38

0

There is _spYield(a,b) in init.js which is declared as:

function _spYield(b, a) {
if (a > 0)
    window.setTimeout(function() {
        _spYield(b, a - 1)
    }
    , 0);
else
    b()

}

answered Oct 31 '15 at 20:38

Danny '365CSI' Engelman

16,526
2
32
49

Chloe · Answer 2 · 2015-10-29T23:03:18.443

-1

I'll skip the part about this being extremely bad practice and to always use timeouts and callbacks.

Because js is single threaded, you don't have many options. I would go with an empty loop, but as @joews says, that will stall the execution, and cacheLoaded will never be set to true;

while (this.cacheLoaded != true) { /*Stall*/ }

EDIT:

Callback Solution:

get: function(key, callback) {
        var fn = function { 
            if(this.cacheLoaded != true) 
                window.setTimeout(fn, 500);
            else
                callback((typeof this[key] != 'undefined' && this[key] == true) ? true : false);
        };
        fn();      
    }

Then call it like so:

Permission.get('ALOW_DELETE', function(result) {if(result) deleteSomething();});

edited Oct 29 '15 at 23:03

answered Oct 29 '15 at 22:52

Chloe

483
4
14

1

That won't work because JS execution will stay on the current call stack. `cacheLoaded` can only be set to true on a later tick of the event loop, which the JS engine will never get to. – joews Oct 29 '15 at 22:54
@joews You're correct. I've noted that and added an actual solution. – Chloe Oct 29 '15 at 23:06

Javascript: Synchronous wait/delay method

2 Answers2