Many small closures versus a single large one

Question

Many small closures versus a single large one

Currently, I have a Google Map set up with various event listeners attached to different elements. For example, I am adding events for a Point object like this:

google.maps.event.addListener(this.marker, 'click', (function(point) {
    return function(event) {
        alert(point.index);
    }})(this));

I have numerous events such as 'click', 'rightclick', 'doubleclick', and more that I need to handle.

Typically, when adding an event listener, I encapsulate only the current point within a closure. However, I am considering simplifying it to:

var point = this;

google.maps.event.addListener(this.marker, 'click', function(event) {
    alert(point.index);
});

I have hesitated to make this change due to a couple of reasons. Firstly, I've observed experienced individuals in JavaScript use "individual" closures, which makes me think there may be a valid reason for it.

Secondly, I am uncertain about how creating a large closure might affect performance by capturing unnecessary variables (e.g., 'var color') that are not required in my event function. Could this potentially lead to performance issues?

Any insights or advice on optimizing these event listeners would be greatly appreciated. Thank you!

javascript closures

Answer 1

Answer №1

Both instances demonstrate the creation of closures around a variable referred to as point. In the first scenario, point serves as a parameter for the outer anonymous function, whereas in the second case, point is a local variable. Nevertheless, both situations involve its encapsulation within an anonymous function.

Forming an anonymous function that takes a named parameter and promptly invokes it with an argument is just one method of associating a value with a specific name within a scope.

(function(x) { 
    // x now holds the assigned value
})(getValue());

Alternatively:

var x = getValue();
// x now contains the specified value

The distinction lies in utilizing a function to ensure that the variable x exists within its unique namespace, distinct from any other occurrences of x in the enclosing scope. This emphasizes maintainability over execution speed.

As for performance comparisons, conducting tests across various browsers is vital since each has its own execution engines.

One might assume that creating more anonymous functions leads to increased small allocations. Hence, the second example, with fewer anonymous functions, could potentially outperform the first. However, such assumptions are baseless without thorough testing on all relevant browsers.

Answer 2

Both instances demonstrate the creation of closures around a variable referred to as point. In the first scenario, point serves as a parameter for the outer anonymous function, whereas in the second case, point is a local variable. Nevertheless, both situations involve its encapsulation within an anonymous function.

Forming an anonymous function that takes a named parameter and promptly invokes it with an argument is just one method of associating a value with a specific name within a scope.

(function(x) { 
    // x now holds the assigned value
})(getValue());

Alternatively:

var x = getValue();
// x now contains the specified value

The distinction lies in utilizing a function to ensure that the variable x exists within its unique namespace, distinct from any other occurrences of x in the enclosing scope. This emphasizes maintainability over execution speed.

As for performance comparisons, conducting tests across various browsers is vital since each has its own execution engines.

One might assume that creating more anonymous functions leads to increased small allocations. Hence, the second example, with fewer anonymous functions, could potentially outperform the first. However, such assumptions are baseless without thorough testing on all relevant browsers.

Answer 3

Answer №2

As long as your point remains constant, there shouldn't be any issues with the code. Your second example should work just fine:

var point = this;

google.maps.event.addListener(this.marker, 'click', function(event) {
  alert(point.index);
});

In cases where your point may change and you need it to be in a specific state, like within a loop for instance, it's recommended to create another closure for your event handling function:

for(var i = 0, len = points.length; i < len; i++) {
  google.maps.event.addListener(points[i].marker, 'click', (function(point) {
    return function(event) {
      alert(point.index);
    }
  })(points[i]));
}

If you didn't use closures in this scenario, the event would have referenced the last elements of the array at the time it was triggered.

Answer 4

As long as your point remains constant, there shouldn't be any issues with the code. Your second example should work just fine:

var point = this;

google.maps.event.addListener(this.marker, 'click', function(event) {
  alert(point.index);
});

In cases where your point may change and you need it to be in a specific state, like within a loop for instance, it's recommended to create another closure for your event handling function:

for(var i = 0, len = points.length; i < len; i++) {
  google.maps.event.addListener(points[i].marker, 'click', (function(point) {
    return function(event) {
      alert(point.index);
    }
  })(points[i]));
}

If you didn't use closures in this scenario, the event would have referenced the last elements of the array at the time it was triggered.

Many small closures versus a single large one

Answer №1

Answer №2

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