Javascript Tip: ‘Number()’ function

Context:

Trying to do a simple number comparison, can be surprising in javascript sometimes. For example…

function fooMethod( fooVariable )
{
    if ( fooVariable > 10 )
    {
        alert('true');
    }
    else
    {
        alert('false');
    }
}

… where fooVariable is a number taken from a form, and hence originally of type string ! Sometimes feeding in the number “5″ may end up evaluating as true… even though it should be false ( 5 > 10 ) !

Solution:

The problem is to do with Javascript being weakly-typed, hence although 5 is smaller than 10, it may be treated as the string 5 rather than than the number 5. The solution is to make use of the convenient ‘Number‘ function provided by javascript (part of the core library). As follows…

function fooMethod( fooVariable )
{
    if ( Number( fooVariable ) > 10 )
    {
        alert('true');
    }
    else
    {
        alert('false');
    }
}

… that’ll ensure that if not already a number type it is converted before the comparison is made. Very nice !

Wa Allahu A’lam