Trim in JavaScript

In JavaScript, there is no trim method. But below i have created a simple trim method which removes the leading and the trailing spaces from the string.

function trim(str) {
    str = str.replace(/^s+/, '')
    for (var i = str.length; i--;)
        if (/S/.test(str.charAt(i)))
            return str.substring(0, ++i)
    return str
}

function testTrim() {
    var myString = " Test Trim ";
    alert(trim(myString));
}