how to validate password allow space in middle of string

function spc(str)
{
var l=str.length;//check length of string
for(var i=0;i<l;i++)
{
if(str[0]==' ' || str[str.length-1]==' ')//check first & last character of password
{
document.getElementById("spa_error").innerHTML='Space key cannot be used for the first or last character of your password';
}else
{
document.getElementById("spa_error").innerHTML='';
}
}
}