What Does the Plus Sign ( ) Do Before a JavaScript Function Expression?

The Plus Sign in JavaScript Function Expressions

In JavaScript, the plus sign ( ) placed before a function expression plays a significant role in its execution.

When the parser encounters a function expression without a leading operator, it interprets it as a function declaration. This can lead to syntax errors if the parser is expecting a statement. However, by adding the sign, the parser is forced to treat the expression as a mathematical expression, which in turn results in a function reference.

The function reference can be immediately invoked by adding parentheses after the expression, as seen in the example:

+function() { console.log("Something.") }()

This line of code defines an anonymous function and executes it immediately. Without the sign, the parser would interpret it as a function declaration, which lacks a name and would result in a syntax error.

The sign is not the only unary operator that can be used for this purpose. Other valid options include -, !, ~, or any other unary operator. Alternatively, parentheses can be used to enclose the function expression, which is more commonly seen:

(function() { console.log("Foo!"); })();
// or
(function() { console.log("Foo!"); }());

By understanding the use of the sign or any other unary operator before a function expression, developers can effectively create immediately invoked functions that facilitate code execution upon encountering the expression.

The above is the detailed content of What Does the Plus Sign ( ) Do Before a JavaScript Function Expression?. For more information, please follow other related articles on the PHP Chinese website!