JavaScript format page numbers like a printer dialog. "1,3,4-7" returns an array [1,3,4,5,6,7]

findPages

function findPages (pages) {
    // usecase =  "1-3,6,9";
    if (typeof(pages) != "string"){ return }; // must be a string
    var splitUse = pages.split(",") // ["1-3","6","9"]
    var patt1 = new RegExp("-");  // search for -
    for (i=0;i < splitUse.length;i++) {
        if ( patt1.test(splitUse[i]) ){ // tests for "-"
            var newsub = splitUse[i].split("-");
            for (n=newsub[0]; n<=newsub[1]; n++){
                splitUse.push(n); // adds contents to end of array
            }
            splitUse.splice(i,1);
        }
        splitUse[i] = parseInt(splitUse[i]); //convert string to number
        if ( isNaN(splitUse[i]) ) { //cleans out any junk NaN from bad entry
            splitUse.splice(i,1);
            i--;
        };
    }
    return splitUse.sort(function(a,b){return a-b}); // [1,2,3,6,9]
}