Calling a javascript function on a php variable

Question

Javascript:

function capitalizeFL(string) { 
 return string.charAt(0).toUpperCase() + string.slice(1);
}

PHP:

echo "You have chosen a <script>document.write(capitalizeFL(".$race."));</script>";

$race contains a string. What I would like is simply to capitalize the first letter of the php variable $race, using the Javascript function above, and print it on the page.

I could find another way of doing this, but this JS-PHP mixing thing is confusing to me and I'd very much like to figure out WHY this doesn't work.

• Waygood: capitalizeFL(my string) needs to be capitalizeFL('my string') so you need to delimit $race with ' to identify it as a string and escape any ' within the text too. e.g. your string could be O'Neil
• Bernard: Why not just use a PHP function to do this. Take a look at the following functions: - string strtoupper(string $string) Except ofcourse there's a specific reason why you are using a javascript function there.
• frrlod: @Bernard as I've mentioned in my question I could find other ways of doing it, just wanted to understand for the sake of learning.

Answer 1

Look at the generated JavaScript.

document.write(capitalizeFL(value_of_race));

That's an identifier, not a string literal. You need to include quote marks in your generated JS.

Given a string, the json_encode function will output the equivalent JS literal (even if it isn't valid JSON). Use that to convert your PHP variables into JS literals.

$js_race = json_encode($race);
echo "You have chosen a <script>document.write(capitalizeFL($js_race));</script>";

• Jace: ie. document.write(capitalizeFL('".$race."'))
• Quentin: @Jace — That will break if the string contains ' characters.
• Quentin: @Waygood — Yes, but Jace's code doesn't do that (and your comment doesn't provide any code to do the escaping). Mine does (although it uses " instead of ').
• frrlod: I don't understand one thing. $race IS a string. Say it contains "human". Then wouldn't value_of_race be "human", already with quotes, rather than just human?
• Quentin: No. Quote marks delimit the start and end of a string literal (in both PHP and JavaScript). They aren't part of the string, they just contain it. If they were, then you would have " characters showing up every time you tried to print anything in PHP, which would be awful.

Answer 2

echo "You have chosen a <script>document.write(capitalizeFL('".$race."'));</script>";

You can try above code. Javascript string must be wrapped by ''.