[JavaScript snippet] string prefix, suffix

prefix_suffix.js

function prefix(str, sep) {
    // prefix("foo.bar.txt", ".") => foo
    return str && str.substring(0, str.indexOf(sep));
}

function suffix(str, sep, excludeSep) {
    // suffix("foo.bar.txt", ".") => .txt
    // suffix("foo.bar.txt", ".", true) => txt
    return str && str.substring(str.lastIndexOf(sep) + (excludeSep === true ? sep.length : 0));
}

function inbetween(str, sep0, sep1) {
    // inbetween("foo.bar.txt", ".", ".") => bar
    // inbetween("foo.txt", ".", ".") => null
    if (!str)
        return null;
    var idx = str.indexOf(sep0);
    if (idx < 0)
        return null;
    str = str.substring(idx + sep0.length);
    idx = str.lastIndexOf(sep1);
    if (idx < 0)
        return null;
    return str.substring(0, idx);
}

Note that the input string may need trimming before calling the methods for a safety reason.

For instance, suffix("hello world! ", " ") --- Note a trailing space! --- may return an unexpected output;

But suffix("hello world! ".trim(), " ") won't.