rename-diff.js

var commonPrefix = function(a, b) {
    if (a === b) return a;
    var i = 0;
    while (a.charAt(i) == b.charAt(i))++i;
    return a.substring(0, i);
}
var commonSuffix = function(a, b) {
    if (a === b) return "";
    var i = a.length - 1,
        k = b.length - 1;
    while (a.charAt(i) == b.charAt(k)) {
        --i;
        --k;
    }
    return a.substring(i + 1, a.length);
}
var renameDiff = function(a, b) {
    var p = commonPrefix(a, b),
        s = commonSuffix(a, b),
        o = a.substring(p.length, a.length - s.length),
        n = b.substring(p.length, b.length - s.length);
    return [p, o, n, s];
}
var formatRenameDiff = function(d) {
    var p = d[0],
        o = d[1],
        n = d[2],
        s = d[3];
    if (o == "" && n == "" && s == "") {
        return p;
    }
    return [p, "{ ", o, " -> ", n, " }", s].join("");
}
formatRenameDiff(renameDiff(
    "lib/DataStores/Wrappers/AbstractHashRangeKeyStore.php",
    "lib/DataStores/Wrappers/CommandHashRangeKeyStoreTrait.php"
));
// "lib/DataStores/Wrappers/{ AbstractHashRangeKeyStore -> CommandHashRangeKeyStoreTrait }.php"