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Asked: 2026-06-17T08:14:01+00:00

I have this javascript code below: <!doctype html> <html lang=en> <head> <meta charset=utf-8 />

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I have this javascript code below:

<!doctype html>
<html lang="en">
    <head>
        <meta charset="utf-8" />
        <title></title>

        <script>
            function Person(first, last) {
                this.first = first;
                this.last  = last;
            }

           Person.prototype.toString = function() { 
                return this.first + this.last;
           }
            var person = new Person("John", "Dough");

            alert(person); // same result since alert calls toString()  

        </script>
    </head>
    <body>
    </body>
</html>

The question is why does the alert(person) display “JohnDough”? To me, alert(person) should not display anything.

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1 Answer

  1. Editorial Team

    When using alert, the method implicitly attempts to call a toString on the object. In your case, toString is defined and does what you expect when explicitly calling toString. If you hadn’t defined toString, alert would have used the native toString method of an Object and returned “[object Object]”, as pointed out by @FelixKling.

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