Question

I have seen a piece of code in the web.

function isMobile() {
var index = navigator.appVersion.indexOf("Mobile");
return (index > -1);
}

Why can’t we just check if index is > or < 0? Please explain returning index > -1.

Answer 1

If the result of indexOf is -1, the string was not found. 0 would indicate that is is in the string, and that it is, in fact, at the start of the string.

Therefore, if you tested for > 0, then you’d be checking if it existed somewhere not at the start of the string. !(index < 0) and index >= 0 would both work, too, but the former is a little more complex than it needs to be.

If you were confused about the syntax, returning the result of a comparison is the same as returning true if the comparison results in true and returning false when the comparison results in false.