Why bother assigning something to be the same as itself?

Question

Why bother assigning something to be the same as itself?

Just came across this question where someone passed

window.Module = window.Module || {}

into a function.

Here's an example:

(function(module){
    // do something with module
})(window.Module = window.Module || {});

I get that if window.Module is not defined (or false), then {} will be passed in. But why set window.Module equal to itself?

For those providing answers:

This is how I interpret the code:

if(!(window.Module = window.Module)) {
     // pass {} into the function
}
else {
     // pass window.Module = window.Module into the function 
     // (which doesn't make sense to me)
}

javascript variables parameters module-pattern

Answer 1

Answer №1

That code snippet serves a dual purpose:

The window.Module || {} part leverages JavaScript's unique logical OR operator to return either the existing window.Module value (if it exists) or an empty object ({}) if it is null or undefined. The result of this operation is then stored back into window.Module. This means that if window.Module was previously not assigned, it will now contain an empty object; on the other hand, if it already had a truthy value, it remains unchanged (although most modern engines optimize this redundant assignment).
Following that, the newly assigned or pre-existing value in window.Module is passed as an argument to the function.

In conclusion, this piece of code ensures that window.Module is initialized to an empty object if it wasn't set before. Regardless of its previous state, the current value held by window.Module is supplied as input to the following function.

Answer 2

That code snippet serves a dual purpose:

The window.Module || {} part leverages JavaScript's unique logical OR operator to return either the existing window.Module value (if it exists) or an empty object ({}) if it is null or undefined. The result of this operation is then stored back into window.Module. This means that if window.Module was previously not assigned, it will now contain an empty object; on the other hand, if it already had a truthy value, it remains unchanged (although most modern engines optimize this redundant assignment).
Following that, the newly assigned or pre-existing value in window.Module is passed as an argument to the function.

In conclusion, this piece of code ensures that window.Module is initialized to an empty object if it wasn't set before. Regardless of its previous state, the current value held by window.Module is supplied as input to the following function.

Answer 3

Answer №2

This is precisely why I prefer the traditional if statement over the short-circuit expression.

When written in a conventional format:

if (!window.Module)
{
    window.Module = {};
}
else
{
    // This section is essentially redundant and can be removed.
    window.Module = window.Module;
}

While this structure cannot be used within an expression, it is much easier to understand.

The primary purpose of assigning window.Module is to ensure its existence. Although you could use window.Module || {}, this would leave it uninitialized.

Answer 4

This is precisely why I prefer the traditional if statement over the short-circuit expression.

When written in a conventional format:

if (!window.Module)
{
    window.Module = {};
}
else
{
    // This section is essentially redundant and can be removed.
    window.Module = window.Module;
}

While this structure cannot be used within an expression, it is much easier to understand.

The primary purpose of assigning window.Module is to ensure its existence. Although you could use window.Module || {}, this would leave it uninitialized.

Answer 5

Answer №3

(function(m){
    // manipulate the module in some way
})(window.Module = window.Module || {});

This snippet of code ensures that a global Module object is defined before passing it into the function. Without the assignment, like so:

(function(m){
    // manipulate the module in some way
})(window.Module || {});

the Module object may not be set if it doesn't exist at that particular moment. While access to the object can still be achieved using m, certain parts of the function might rely on Module.

A more effective approach could be:

// global scope
if (!window.Module) window.Module = {};

(function () {
  // utilize Module here
}());

Answer 6

(function(m){
    // manipulate the module in some way
})(window.Module = window.Module || {});

This snippet of code ensures that a global Module object is defined before passing it into the function. Without the assignment, like so:

(function(m){
    // manipulate the module in some way
})(window.Module || {});

the Module object may not be set if it doesn't exist at that particular moment. While access to the object can still be achieved using m, certain parts of the function might rely on Module.

A more effective approach could be:

// global scope
if (!window.Module) window.Module = {};

(function () {
  // utilize Module here
}());

Why bother assigning something to be the same as itself?

Answer №1

Answer №2

Answer №3

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