if sub string == code example

Example: check if string contains substring

Like this:

if (str.indexOf("Yes") >= 0)
...or you can use the tilde operator:

if (~str.indexOf("Yes"))
This works because indexOf() returns -1 if the string wasn't found at all.

Note that this is case-sensitive.
If you want a case-insensitive search, you can write

if (str.toLowerCase().indexOf("yes") >= 0)
Or:

if (/yes/i.test(str))