CODEWITHSUNDEEP
javascript
jcfrei
jcfrei

Reputation: 1809

explain javascript: value assignment fails

var sc = new stuCore();
function stuCore() {
    this.readyPages = [];
    this.once = true;
    var self = this;

    // gets called asynchronously
    this.doPrepPage = function (page){

            if(self.once == true){
                   // still gets executed every time, assignment fails
                   self.once = false;
                   doSomeStuffOnce();
            }
    };

   this.addReadyPage = function (pageid) {

            console.log("readypage called");
            this.readyPages.push(pageid);
            if (!$.inArray(pageid, self.readyPages) != -1) {
                    this.doPrepPage(pageid);
            }
    };


}

why does this assignment fail? I thought I knew the basics of js, but I'm stumped by this. And furthermore what would be a possible solution? call a constructor first and set the variable there?

EDIT: gets called like this in some other script:

  sc.addReadyPage(self.id);

Upvotes: 3

Views: 239

Answers (2)

steveukx
steveukx

Reputation: 4368

The jQuery.inArray function will return the index in the containing array for the given value. Your script pushes pageid into this.readyPages before checking whether it exists in self.readyPages. this.readyPages and self.readyPages are the same array reference, so the result will always be zero or greater, so the condition that calls doPrepPage will never run.

You could try switching their order around:

this.addReadyPage = function (pageid) {
        console.log("readypage called");
        if ($.inArray(pageid, self.readyPages) != -1) {
                this.readyPages.push(pageid);
                this.doPrepPage(pageid);
        }
};

(edit: Removed the additional !, thanks @chumkiu)

Upvotes: 1

CKKiller
CKKiller

Reputation: 1422

If I understand correctly you're calling this.doPrepPage as <insert variable name here>.doPrepPage?

If this is the case then your var self passes through to the anonymous function and is stored there, so everytime you call this.doPrepPage it takes the local variable of self.

Try setting self to a global variable, this way it will permanently modify self so each time this.doPrepPage is called it uses the updated variable.

Upvotes: 0

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