Welcome!

Apache Authors: Elizabeth White, Pat Romanski, Liz McMillan, Christopher Harrold, Janakiram MSV

Related Topics: Release Management , Microsoft Cloud, Machine Learning

Release Management : Article

AJAXWorld RIA Conference - Speaker Mike Girouard's JavaScript Design Patterns, #1

Self-invocation - one of the most useful and commonplace patterns

Mike Girouard's Blog

I would like to begin this special series in the run-up to AJAXWorld RIA Conference & Expo in October with one of the most useful and commonplace patterns in my code. Arguably, this can be considered a feature of the JavaScript language rather than a design pattern; however, when considering the contexts in which it is applied, I regard it as a pattern. Self-invocation (also known as auto-invocation) is when a function executes immediately upon it’s definition. This is a core pattern and serves as the foundation for many other patterns of JavaScript development.

Motivation

The primary motivation behind self-invoking functions is to create scope. In JavaScript, only functions have scope. Any time variables are defined outside of a function, they are carelessly dumped into the global object.

Implementation

A self-invoking function is a standard function, just with a set of parentheses appended to the end.

function () {
var foo = 'Hello';
var bar = 'world';
var baz = [foo, bar];
alert
(baz.join(', '));
}();

The above example defines an anonymous function. This creates a literal function, yet since no name is attributed to it, the value is never stored. The trailing parenthesis tell the function to execute, just as if you were calling a named function.

Upon execution, the above function creates three variables, formats them, and alerts them to the user. Once the function terminates, the variables are discarded and the global object remains unchanged.

Distinguishing from Actual Functions

Given the oddness of the pattern (and lack of widespread understanding), it is very possible for developers to misinterpret this pattern as an actual function. It it recommended that an extra set of parentheses wrap the function definition as well so to provide a visual clue to the developer that the function isn’t a normal function. The result would be as follows.

(function () {

var foo = 'Hello';
var bar = 'world';
var baz = [foo, bar];
alert
(baz.join(', '));

})();

Passing Parameters

In the event where a self-invoking function requires parameters, they can be passed in the same manor that you would a regular function.

The following example applies an “negative” class on every input element who’s numeric value is below 0.

(function (elements) {

for (var i = 0; i < elements.length; i++) {
if ((elements[i].value * 1) < 0) {
elements
[i].className = 'negative';
}
};

})(document.getElementsByTagName('input'));

Executing in Another Scope

Even though the function is executing within its own local scope, the this keyword will still refer to the global object.

The following example uses the Function.call() method to execute a self-invoking function within the scope of the first table element on the page.

(function (elements) {

for (var i = 5; i < this.rows.length; i++) {
this.rows[i].className = 'hide';
}

}).call(document.getElementsByTagName('table')[0]);

Conclusion

In an effort to protect the global object, all JavaScript applications should be written within a self-invoking function. This will create an application scope in which variables can be created without the fear of them colliding with other applications.

If a global variable is needed, developers must take the extra step by setting them directly within the window object. For example window.foo = ‘bar’;.

Self-invocation is a fundamental pattern of professional JavaScript development. Nearly every pattern in this weeks catalog uses it as a base to create scope, closure, or to configure cross-platform objects on-the-fly.

More Stories By Michael Girouard

Mike Girouard is a front-end web developer living in New York City. As the Sr. Developer at the creative agency Magnani Caruso Dutton, he takes pride in his ability to introduce web standards and beautiful code to industry giants such as Discover and AT&T. In his offtime, Girouard goes right back to his editor and codes toward his latest open-source baby, Panda PHP Components. You can read more about him and his other projects on his blog, http://www.lovemikeg.com/blog.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


IoT & Smart Cities Stories
Every organization is facing their own Digital Transformation as they attempt to stay ahead of the competition, or worse, just keep up. Each new opportunity, whether embracing machine learning, IoT, or a cloud migration, seems to bring new development, deployment, and management models. The results are more diverse and federated computing models than any time in our history.
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
Digital Transformation is much more than a buzzword. The radical shift to digital mechanisms for almost every process is evident across all industries and verticals. This is often especially true in financial services, where the legacy environment is many times unable to keep up with the rapidly shifting demands of the consumer. The constant pressure to provide complete, omnichannel delivery of customer-facing solutions to meet both regulatory and customer demands is putting enormous pressure on...
IoT is rapidly becoming mainstream as more and more investments are made into the platforms and technology. As this movement continues to expand and gain momentum it creates a massive wall of noise that can be difficult to sift through. Unfortunately, this inevitably makes IoT less approachable for people to get started with and can hamper efforts to integrate this key technology into your own portfolio. There are so many connected products already in place today with many hundreds more on the h...
The standardization of container runtimes and images has sparked the creation of an almost overwhelming number of new open source projects that build on and otherwise work with these specifications. Of course, there's Kubernetes, which orchestrates and manages collections of containers. It was one of the first and best-known examples of projects that make containers truly useful for production use. However, more recently, the container ecosystem has truly exploded. A service mesh like Istio addr...
Digital Transformation: Preparing Cloud & IoT Security for the Age of Artificial Intelligence. As automation and artificial intelligence (AI) power solution development and delivery, many businesses need to build backend cloud capabilities. Well-poised organizations, marketing smart devices with AI and BlockChain capabilities prepare to refine compliance and regulatory capabilities in 2018. Volumes of health, financial, technical and privacy data, along with tightening compliance requirements by...
Charles Araujo is an industry analyst, internationally recognized authority on the Digital Enterprise and author of The Quantum Age of IT: Why Everything You Know About IT is About to Change. As Principal Analyst with Intellyx, he writes, speaks and advises organizations on how to navigate through this time of disruption. He is also the founder of The Institute for Digital Transformation and a sought after keynote speaker. He has been a regular contributor to both InformationWeek and CIO Insight...
Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settlement products to hedge funds and investment banks. After, he co-founded a revenue cycle management company where he learned about Bitcoin and eventually Ethereal. Andrew's role at ConsenSys Enterprise is a mul...