How Does 'var FOO = FOO || {};' Create and Manage Namespaces in JavaScript?

Namespaces in JavaScript: Understanding "var FOO = FOO || {}"

In JavaScript, it is common to see the following code at the beginning of source files:

This code uses the conditional operator (||) to assign an empty object ({}) to a variable (FOO) if it does not already exist. This technique is often employed to create namespaces, which are named objects used to organize functions and variables.

The conditional operator works as follows: if the variable FOO is undefined or null (which is the initial state), the empty object is assigned to it. However, if FOO has already been defined, its existing value will be used.

By using a namespace, multiple files sharing the same namespace can define functions and variables without contaminating the global object. For instance, consider the following two files:

File 1:

File 2:

In this case, both files share the MY_NAMESPACE namespace. Therefore, no matter the order in which they are loaded, both func1 and func2 will be defined within the MY_NAMESPACE object. The first file creates the initial namespace, while subsequent files augment the existing object, ensuring consistent object structure across files.

This technique is particularly useful for asynchronous script loading where the order of script execution is uncertain. By ensuring that all scripts sharing a namespace use the same object, the order of file loading does not affect the integrity of the defined objects.

The above is the detailed content of How Does 'var FOO = FOO || {};' Create and Manage Namespaces in JavaScript?. For more information, please follow other related articles on the PHP Chinese website!