var str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
var regexp = /[A-E]/gi;
var matches_array = str.match(regexp);
console.log(matches_array);
// ['A', 'B', 'C', 'D', 'E', 'a', 'b', 'c', 'd', 'e']
const array = ["page=4", "sortOrder=asc", "datePosted=all-time", "sortOrder=desc"];
const match = array.find(value => /^sortOrder=/.test(value));
// match = "sortOrder=asc"
yourString.match(RegExp(/YOUR REGEX/))