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copied!<p>Yes <a href="http://es5.github.com/#x7.9" rel="nofollow">ECMA Spec</a>, which is the Javascript spec, defines the behavior like this</p> <blockquote> <p>Certain ECMAScript statements (empty statement, ... <strong>return statement</strong>, and throw statement) must be terminated with semicolons. Such semicolons may always appear explicitly in the source text. <strong>For convenience</strong>, however, such <strong>semicolons may be omitted</strong> from the source text in certain situations. These situations are described by saying that <strong>semicolons are automatically inserted</strong> into the source code token stream in those situations.</p> </blockquote> <p>Further more</p> <blockquote> <p>When a continue, break, return, or throw token is encountered and a LineTerminator is encountered before the next token, a semicolon is automatically inserted after the continue, break, return, or throw token.</p> <p>An <strong>Expression in a return</strong> or throw statement <strong>should start on the same line as the return or throw token.</strong></p> </blockquote> <p>And they have given an <strong>example</strong> of:</p> <p>The source</p> <pre><code>return a + b </code></pre> <p>is transformed by automatic semicolon insertion into the following:</p> <pre><code>return; a + b; </code></pre> <hr> <p>So your first code will be interpreted as: </p> <pre><code>return; this.firstName() + " " + this.lastName(); </code></pre> <p>with the automatically added semi colon at the end of return.</p> <hr> <p>So the spec gives practical advice to face these situations in general javascript:</p> <blockquote> <p>A postfix <strong>++</strong> or <strong>--</strong> operator should appear on the same line as its operand.</p> <p>An Expression in a <strong>return</strong> or <strong>throw</strong> statement should start on the same line as the return or throw token.</p> <p>A Identifier in a <strong>break</strong> or <strong>continue</strong> statement should be on the same line as the break or continue token.</p> </blockquote>

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