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guide/english/javascript/singleton-in-javascript/index.md

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+---
+title: Creating a Singleton in JavaScript
+---
+
+## Creating a Singleton in JavaScript
+
+A singleton is an object that only allows one instance of itself to be created and allows a global point of access to it. The singleton design pattern can be useful if you have some data that should remain the same throughout your application.
+
+### Let's Get Started
+
+Let's create an object with an immediately-invoked function expression (or _IIFE_, pronounced "iffy") that will give us the effect of a singleton.
+
+```
+var singletonFn = (function(){ // Created IIFE Function
+  var dataCounter = 0;
+  return { // Any code inside this return stuff will be accessible directly using objectname.
+    
+    getDataCounter: function(){
+      return dataCounter;
+    },
+  
+    setDataCounter: function(val){
+      dataCounter = val;
+    },
+    
+    fishNames: ["SimpleFish"] // Can create variables, arrays, etc.
+  }
+})();
+
+console.log(singletonFn.getDataCounter()); // 0 by default
+
+singletonFn.setDataCounter(20);
+
+console.log(singletonFn.getDataCounter()); // 20
+
+console.log(singletonFn.fishNames); // ["SimpleFish"]
+```
+
+Here's another example of a singleton:
+
+```
+var Person;
+
+(function() {
+  let instance;
+
+  Person = function(fName, lName, job) {
+    // constructor
+    this.fName = fName || 'John';
+    this.lName = lName || 'Doe';
+    this.job = job || 'Software Engineer';
+    
+    if (!instance) {
+      instance = this;
+    }
+
+    this.getFullName = function () {
+      return this.fName + ' ' + this.lName;
+    }
+    
+    this.getJob = function () {
+      return this.job;
+    }
+
+    this.print = function () {
+      console.log(this.getFullName() + ' ' + this.getJob());
+    }
+
+    return instance;
+  }
+})();
+
+//initialize these "guys" but they point to the same object
+var guy1 = new Person();
+var guy2 = new Person();
+
+// proof that they're the same instance
+guy1.print(); // "John Doe Software Engineer"
+guy2.print(); // "John Doe Software Engineer"
+console.log(guy1 == guy2); //true
+
+// modify guy2 and see that guy1 has changed as well
+guy2.fName = 'Jane';
+guy2.lName = 'Doo';
+guy2.job = 'Project Manager';
+guy1.print(); // "Jane Doo Project Manager"
+guy2.print(); // "Jane Doo Project Manager"
+```