JavaScript Array.filter()

Question

The Array.filter() method is having an asynchronous behavior. According to the documentation, it seems to me it's not supposed to work that way.

Moreover,it does not allow the reference to a callback, as usual in such cases.

I am limited in relation to the use of libraries, but also confuses me, how it reacts that way.

I am not also expert in ECMAScript, am i making some mistake?

I just want to filter one array and send the results to a HTML select element as several options.

I have something like this:

var selCompanyDeps = departments.filter(fromSelectedCompany);

fillSelect($("#selDeparts"), selCompanyDeps, 'departmentID', 'name', selectedID);

function fromSelectedCompany(value){
    var selectedCompany = $( "#SelComps" ).val();
    return (value.companyID===Number(selectedCompany));
}

Thanks

It does not provide a callback because it is not asynchronous. I cannot discern a question here. — Alex Booker
– Alex Booker, Commented Aug 3, 2015 at 18:09
Yes, i saw .filter wasn´t an async method tymeJV, and that's my question Petrichor. — Pedro Guedes
– Pedro Guedes, Commented Aug 4, 2015 at 7:22

Toothbrush · Accepted Answer · 2015-08-03 18:58:52Z

7

Array.filter is not an asynchronous method, but what you appear to be confusing is the order of execution of a JavaScript programme.

When the browser parses your code, the browser will look for named functions and add them to the list of declared names in the current scope (known as function hoisting).

Therefore, fromSelectedCompany is executed before you call fillSelect, so your code is equivalent to the following:

function fromSelectedCompany(value){
    var selectedCompany = $( "#SelComps" ).val();
    return (value.companyID===Number(selectedCompany));
}

var selCompanyDeps = departments.filter(fromSelectedCompany);

fillSelect($("#selDeparts"), selCompanyDeps, 'departmentID', 'name', selectedID);

answered Aug 3, 2015 at 18:58

Toothbrush

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3 Comments

Pedro Guedes Over a year ago

Thanks toothbrush, i knew about hoisting, i didn't knew there was also function hoisting.

Pedro Guedes Over a year ago

Great!! It's working. I just put the function as anonymous function inside the .filter, and it solves the question. One more time, thanks @toothbrush, and thanks everyone who was trying to help var selCompanyDeps = departments.filter(function (value){ var selectedCompany = $( "#SelComps" ).val(); return (value.companyID===Number(selectedCompany)); });

Toothbrush Over a year ago

@PedroGuedes OK, glad to have been of help.

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