Comparing 1.3.52 and 1.3.54 as strings and as numbers

Question

I am wondering why the following works:

oldversion = "1.3.52";
newversion = "1.3.54";

if (newversion > oldversion) {
    console.log('test');
}

but this does not:

if (1.3.54 > 1.3.52) {
    console.log('test');
}

I know that the last example won't work because they are not actual numbers. But I am trying to find out what JavaScript is doing when it encounters a string with a number in it.

This is what I found on W3Schools' JavaScript Comparison and Logical Operators page:

When comparing a string with a number, JavaScript will convert the string to a number when doing the comparison.

So how come it converts the string to a number and suddenly I am not getting an Uncaught SyntaxError: Unexpected number anymore?

Answer 1

You could use a function which iterates the segments.

function checkVersion(a, b) {
    var aa = a.split('.').map(Number),
        bb = b.split('.').map(Number),
        i,
        r = 0,
        l = Math.max(aa.length, bb.length);

    for (i = 0; !r && i < l; i++) {
        r = (aa[i] || 0) - (bb[i] || 0);
    }
    return r;
}

var oldversion = "1.3.52",
    newversion = "1.3.54";

if (checkVersion(newversion, oldversion) > 0) {
    console.log('test');
}