Untested, but this might work without having to pull any libraries in:

    $string .= $cgi->textfield(
        -name      => 'name',
        -default   => 'def',
        -override  => 0,
        -size      => 20,
        -maxlength => 120, 
        -onfocus   => "if (null == this.changed) this.value = ''",
        -onblur    => "if (null == this.changed) this.value = 'def'",
        -onchange  => "this.changed = true",
    );
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