Javascript Validate a comma exists in a field

[crm_user]

This is pretty simple (manager thinking, not me ) but I need to be able to validate that a field has a comma, that's it, that simple. How would I set this up?

[chenyaniv]

it shuold go somthing like that:

function check_comma(str)
{
if(str.indexof(",")==-1)
alert("insert a comma");
}