Question

I have multiple instances of the following code.

var start_time = new Date().getTime();
setTimeout(function timeout(){
    var current_time = new Date().getTime();
    if(some_condition){
        // do stuff
    }else if(start_time - current_time > 10000){
        console.error("... request is timing out.");
    }else{
        setTimeout(timeout, 30);
    }
}, 1);

I want to abstract it to something like

globalLibrary = {

    timeout : function(name, condition, callback, repeat){
        if(typeof repeat !== "number")
            repeat = 30;


        setTimeout(function timeout(){
            var current_time = new Date().getTime();
            if(condition){
                callback();
            }else if(start_time - current_time > 10000){
                console.error(name + " request is timing out.");
            }else{
                setTimeout(timeout, repeat);
            }
        }, 1);

    }
}

// .... somewhere else (not in global scope.)
// There are vars here that are used in the condition and in the callback function.
// They will change due to processes happening elsewhere. 
// eg ajax requests and iframe sendMessages being received.
globalLibrary.timeout(
    "something",
    condition,
    function(){
        // do stuff.
    }       
);

How do I do this so that the condition is rerun with each iteration?
The condition may include multiple ands and ors.

(I’m not using setInterval due to subtle differences in the timing.)

Answer 1

Basically, you want lazy evaluation of the condition. This is easy implemented in languages supporting functional programming by creating a nullary function, which is evaluated when the value is needed.

globalLibrary = {
    timeout: function(name, condition, callback, repeat){
        if(typeof repeat !== "number")
            repeat = 30;

        setTimeout(function timeout(){
            var current_time = new Date().getTime();
            if ( condition() ) { // Note: 'condition' is called
                callback();
            } else if (start_time - current_time > 10000) {
                console.error(name + " request is timing out.");
            } else {
                setTimeout(timeout, repeat);
            }
        }, 1);
    }
}

globalLibrary.timeout(
    "something",
    function () {return condition},
    function(){
        // do stuff.
    }       
);