Return an empty array if string == ""

Question

I'm rewriting my old table sort library. In the library, I have this method which gets some attributes from the table:

<table data-sort-cols="" data-sort-orders="">

getSortInfo : function(element) {
    switch (element.tagName) {
        case "TABLE":
            function getSortAttr(element, attr) {
                var info = element.getAttribute(attr);
                if (info != "") {
                    info = info.split(",").map(function(val) { return parseInt(val,10) });
                } else {
                    info = [];
                }
                return info;
            };
            return {
                columns : getSortAttr(element, "data-sort-cols"),
                orders  : getSortAttr(element, "data-sort-orders"),
            }

I want to shorten the getSortAttr function. Function returns the assigned value (e.g. "1,3,2" -> [1,3,2]). If there is not an assigned value to the attribute, it returns an empty array. I want to get rid of the if statement.

Is there a way to modify this line, and make it return an empty array if the string is empty ""?

info = info.split(",").map(function(val) { return parseInt(val,10) });

I've tried

// returns [NaN]
"".split(",").map(function(val) {
    return parseInt(val, 10);
})

// returns [undefined]
"".split(",").map(function(val) {
    var num = parseInt(val, 10);
    if (!isNaN(num) && isFinite(num)) {
        return num;
    }
})

but didn't work.

Til ES6, that function declaration is invalid in that position. Better move it outside of the switch statement. — Bergi
– Bergi, Commented May 19, 2016 at 23:56
Originally, it's outside the switch statement, declared as another method of the main object. Testing things atm. Thanks for the notice though. — akinuri
– akinuri, Commented May 20, 2016 at 0:00
Why do you want to get rid of the if statement? Checking the input once before the map seems better than using a filter as in the accepted answer, since that unnecessarily checks all the elements of the array. — Barmar
– Barmar, Commented May 20, 2016 at 1:49
@Barmar data-sort-x attributes are set at the initialization stage and getSortInfo method is called when the user clicks on a column header. data-sort-x is set to empty strings before any sorting; after a sort, it changes to "2,1" (column indexes or orders). If statement required for the first sorting. After that I thought it is redundant ... Though I'm not sure if what I'm looking for is a good practice. — akinuri
– akinuri, Commented May 20, 2016 at 11:41
The answer you accepted performs the test on every sort. It just tests in a different way. — Barmar
– Barmar, Commented May 20, 2016 at 15:36

James111 · Accepted Answer · 2016-05-19 23:54:25Z

1

The following function will check if info == "", if info == "", it will then return an empty array, if not, it will split the info string and map it. This is called a shorthand if statement.

info = (info == "") ? [] : info.split(",").map(function(val) { return parseInt(val,10) });

You can also add more conditions to the shorthand condition, e.g:

(info == "" || info != undefined || info != null)

If the above info == "" doesn't work, this might mean that info is undefined. To combat this we can use the following statement:

(typeof(info) != undefined)

answered May 19, 2016 at 23:54

James111

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Comments

Bergi · Accepted Answer · 2016-05-19 23:59:24Z

0

You can use

function getSortAttr(element, attr) {
   return (element.getAttribute(attr) || "").split(",").filter(Boolean).map(Number);
}

to filter out empty strings from the array before mapping them to numbers.

answered May 19, 2016 at 23:59

Bergi

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2 Comments

akinuri Over a year ago

This seems to do the job. I've omitted the || part and used element.getAttribute(attr).split(",").filter(Boolean).map(Number), because the attribute is already set to an empty string before any function call. It's dynamically modifed later.

Bergi Over a year ago

OK, I wasn't sure whether the attributes always existed. Better be safe than sorry :-)

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