Do Curly Braces in JavaScript Alter Function Results Based on Their Placement?

Placement of Curly Braces: A Significant Factor in JavaScript Results

In JavaScript, the placement of curly braces can noticeably alter the output of a code snippet. Consider the following two examples:

<code class="javascript">function test() {
  return
  { /* <- curly brace on a new line */
    javascript: "fantastic"
  };
}</code>

<code class="javascript">function test() {
  return { /* <- curly brace on the same line */
    javascript: "fantastic"
  };
}</code>

When the opening curly brace is on a new line, as in the first example, the code returns 'undefined'. This is because JavaScript's automatic semicolon insertion feature interprets the 'return' statement as an expression statement, so no curly braces are necessary. The code becomes effectively:

<code class="javascript">function test() {
  return;
  {
    javascript: "fantastic"
  };
}</code>

However, when the curly brace is on the same line as 'return', the code returns an object with a 'javascript' property. In this case, the curly braces define the object that is returned by the function.

This behavior is consistent with JavaScript's syntax for object literals. When an object literal is used as a statement, it must be contained within parentheses to avoid conflicts with automatic semicolon insertion. For example:

<code class="javascript">var obj = ({
  javascript: "fantastic"
});</code>

Understanding the subtle implications of curly brace placement can significantly improve the accuracy and reliability of JavaScript code.

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