SYS-CON MEDIA Authors: Liz McMillan, Elizabeth White, Maria C. Horton, Andy Thurai, Zakia Bouachraoui

Blog Feed Post

Node.js ABC’s - G is for Globals

variableGlobalA variable is a storage location paired with an associated name, which contains the information known as a value.  Nearly every programming language under the sun supports variables in some form or another.

Within the context of a single piece of code, the use of variables are straight forward: Store a value, retrieve a value, use the value.

var sum = 1 + 2;
console.log("The sum is " + sum);

The concept is nice and tidy within the context of a single code segment.  But not many software programs are a limited to a single instance.  With object oriented and modular programming where code logic is broken into smaller segments to enable code reuse and inheritance, sharing variables can be cumbersome.

Variable Scope

The concept of where variables are available and accessible is referred to as the variables context, or scope.  When you declare a variable, the section of code it is included in is referred to as local scope.  If you want to share a variable with different contexts (local scopes), you will need to use a global variable that lives within global scope.  Different languages use different constructs to get at global variables. 

Javascript will first look for a local scoped variable and if not found look for a global scoped one and use that.  The following example shows a global "sum" with various functions taking in as parameters,

var sum = 3;
console.log("SUM 1: " + sum);
function printSum2() {
  var sum = 5;
  console.log("SUM 2: " + sum);
}
printSum2();
console.log("SUM 2.5: " + sum);
function printSum3(sum) {
  sum = 6;
  console.log("SUM 3: " + sum);
}
printSum3(sum);
console.log("SUM 3.5: " + sum);
function printSum4(sum) {
  var sum = 7;
  console.log("SUM 4: " + sum);
}
printSum4(sum);
console.log("SUM 4.5: " + sum);

function printSum5() {
  sum = 9;
  console.log("SUM 5: " + sum);
}
printSum5();
console.log("SUM 5.5: " + sum);

Will result in the following output:

SUM 1  : 3
SUM 2  : 5
SUM 2.5: 3
SUM 3  : 6
SUM 3.5: 3
SUM 4  : 7
SUM 4.5: 3
SUM 5  : 9
SUM 5.5: 9

A problem arises when you have a local variable and a global variable with the same name and you wish to control which variable you are accessing.  Node.js has a solution for this with the "global" object.

The Global Object

Just as JavaScript in web browsers has the "window" object that is accessible to all code contexts as a global object, Node has a similar global-level object but is aptly named "global". 

global.sum = 3;
function printSum() {
  var sum = 5;
  console.log("Local Sum: " + sum);
  console.log("Global Sum: " + global.sum);
}

 

Local Sum: 5
Global Sum: 3

With the global object, you can initialize the variable in one context (function) and access it in another like the following:

function printSum() {
  global.sum = 3;
  console.log("Global Sum 1: " + global.sum);
}
function printSum2() {
  console.log("Global Sum 2: " + global.sum);
}
printSum();
printSum2();

 

Global Sum 1: 3
Global Sum 2: 3

There are semi-religious wars going on as to whether the global variables should never be used or are a necessary evil.  I fall in the later camp but do make sure you use them wisely and understand the context from which your variables are run to avoid debugging headaches later down the road.

Read the original blog entry...

More Stories By Joe Pruitt

Joe Pruitt is a Principal Strategic Architect at F5 Networks working with Network and Software Architects to allow them to build network intelligence into their applications.

Latest Stories
The Software Defined Data Center (SDDC), which enables organizations to seamlessly run in a hybrid cloud model (public + private cloud), is here to stay. IDC estimates that the software-defined networking market will be valued at $3.7 billion by 2016. Security is a key component and benefit of the SDDC, and offers an opportunity to build security 'from the ground up' and weave it into the environment from day one. In his session at 16th Cloud Expo, Reuven Harrison, CTO and Co-Founder of Tufin, ...
Historically, some banking activities such as trading have been relying heavily on analytics and cutting edge algorithmic tools. The coming of age of powerful data analytics solutions combined with the development of intelligent algorithms have created new opportunities for financial institutions. In his session at 20th Cloud Expo, Sebastien Meunier, Head of Digital for North America at Chappuis Halder & Co., discussed how these tools can be leveraged to develop a lasting competitive advantage ...
While the focus and objectives of IoT initiatives are many and diverse, they all share a few common attributes, and one of those is the network. Commonly, that network includes the Internet, over which there isn't any real control for performance and availability. Or is there? The current state of the art for Big Data analytics, as applied to network telemetry, offers new opportunities for improving and assuring operational integrity. In his session at @ThingsExpo, Jim Frey, Vice President of S...
"We were founded in 2003 and the way we were founded was about good backup and good disaster recovery for our clients, and for the last 20 years we've been pretty consistent with that," noted Marc Malafronte, Territory Manager at StorageCraft, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm. In their Day 3 Keynote at 20th Cloud Expo, Chris Brown, a Solutions Marketing Manager at Nutanix, and Mark Lav...
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. 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 settl...
"At the keynote this morning we spoke about the value proposition of Nutanix, of having a DevOps culture and a mindset, and the business outcomes of achieving agility and scale, which everybody here is trying to accomplish," noted Mark Lavi, DevOps Solution Architect at Nutanix, in this SYS-CON.tv interview at @DevOpsSummit at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
According to the IDC InfoBrief, Sponsored by Nutanix, “Surviving and Thriving in a Multi-cloud World,” multicloud deployments are now the norm for enterprise organizations – less than 30% of customers report using single cloud environments. Most customers leverage different cloud platforms across multiple service providers. The interoperability of data and applications between these varied cloud environments is growing in importance and yet access to hybrid cloud capabilities where a single appl...
@CloudEXPO and @ExpoDX, two of the most influential technology events in the world, have hosted hundreds of sponsors and exhibitors since our launch 10 years ago. @CloudEXPO and @ExpoDX New York and Silicon Valley provide a full year of face-to-face marketing opportunities for your company. Each sponsorship and exhibit package comes with pre and post-show marketing programs. By sponsoring and exhibiting in New York and Silicon Valley, you reach a full complement of decision makers and buyers in ...
In today's always-on world, customer expectations have changed. Competitive differentiation is delivered through rapid software innovations, the ability to respond to issues quickly and by releasing high-quality code with minimal interruptions. DevOps isn't some far off goal; it's methodologies and practices are a response to this demand. The demand to go faster. The demand for more uptime. The demand to innovate. In this keynote, we will cover the Nutanix Developer Stack. Built from the foundat...
"Cloud computing is certainly changing how people consume storage, how they use it, and what they use it for. It's also making people rethink how they architect their environment," stated Brad Winett, Senior Technologist for DDN Storage, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
Sold by Nutanix, Nutanix Mine with Veeam can be deployed in minutes and simplifies the full lifecycle of data backup operations, including on-going management, scaling and troubleshooting. The offering combines highly-efficient storage working in concert with Veeam Backup and Replication, helping customers achieve comprehensive data protection for all their workloads — virtual, physical and private cloud —to meet increasing business demands for uptime and productivity.
Two weeks ago (November 3-5), I attended the Cloud Expo Silicon Valley as a speaker, where I presented on the security and privacy due diligence requirements for cloud solutions. Cloud security is a topical issue for every CIO, CISO, and technology buyer. Decision-makers are always looking for insights on how to mitigate the security risks of implementing and using cloud solutions. Based on the presentation topics covered at the conference, as well as the general discussions heard between sessio...
"NetApp's vision is how we help organizations manage data - delivering the right data in the right place, in the right time, to the people who need it, and doing it agnostic to what the platform is," explained Josh Atwell, Developer Advocate for NetApp, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
A look across the tech landscape at the disruptive technologies that are increasing in prominence and speculate as to which will be most impactful for communications – namely, AI and Cloud Computing. In his session at 20th Cloud Expo, Curtis Peterson, VP of Operations at RingCentral, highlighted the current challenges of these transformative technologies and shared strategies for preparing your organization for these changes. This “view from the top” outlined the latest trends and developments i...