JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = [
    "2 xxx",
    "20 axxx",
    "38 xxxx",
    "20 bx",
    "8540 xxxxxx"
    ];

arr.sort(function(a, b) {
    var aParts = a.split(" "),
        bParts = b.split(" "),
        aNum = +aParts[0],
        bNum = +bParts[0],
        aText = aParts[1],
        bText = bParts[1];
    if (aNum > bNum)
        return -1;
    else if (aNum < bNum)
        return 1;
    else
        return aText.localeCompare(bText);
});

console.log(arr);