Does Curly Brace Placement Matter in JavaScript Function Returns?

Impact of Curly Brace Placement on JavaScript Function Results

In JavaScript, the placement of curly braces within functions can significantly affect the code's behavior. Consider the following two examples:

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

var r = test();
try {
  alert(r.javascript);
} catch (e) {
  alert('no - it broke: ' + typeof r);
}</code>

In this case, the test() function returns undefined and an alert message of "no - it broke: undefined" is displayed. However, if the curly brace is placed on the same line as return, as shown below:

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

var r = test();
try {
  alert(r.javascript);
} catch (e) {
  alert('no - it broke: ' + typeof r);
}</code>

The test() function will return an object and the alert message will display "fantastic".

This discrepancy stems from JavaScript's automatic semicolon insertion. When a line does not end with a semicolon, but could potentially mark the end of a statement, JavaScript automatically inserts one. Consequently, the first code snippet is effectively interpreted as:

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

The semicolon after return; terminates the return statement, causing the curly brace block to become unreachable code. Thus, test() returns undefined.

In contrast, the second example does not trigger automatic semicolon insertion, resulting in a valid object return value. This is equivalent to the following code:

<code class="javascript">function test() {
    var myObject = new Object();
    myObject.javascript = "fantastic";
    return myObject;
}</code>

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