Change var to const (#700)

tutorials/learn-js.org/en/Variables and Types.md

@@ -5,9 +5,9 @@ Like almost every dynamic language, JavaScript is a "duck-typed" language, and t
 
 We can define several types of variables to use in our code:
 
-    var myNumber = 3;                   // a number
-    var myString = "Hello, World!"      // a string
-    var myBoolean = true;               // a boolean
+    const myNumber = 3;                   // a number
+    const myString = "Hello, World!"      // a string
+    const myBoolean = true;               // a boolean
 
 A few notes about variable types in JavaScript:
 
@@ -16,19 +16,19 @@ A few notes about variable types in JavaScript:
 
 There are two more advanced types in JavaScript. An array, and an object. We will get to them in more advanced tutorials.
 
-    var myArray = [];                    // an array
-    var myObject = {};                  // an object
+    const myArray = [];                    // an array
+    const myObject = {};                  // an object
 
 On top of that, there are two special types called `undefined` and `null`.
 
 When a variable is used without first defining a value for it, it is equal to undefined. For example:
 
-    var newVariable;
+    const newVariable;
     console.log(newVariable); //prints undefined
 
 However, the `null` value is a different type of value, and is used when a variable should be marked as empty. `undefined` can be used for this purpose, but it should not be used.
 
-    var emptyVariable = null;
+    const emptyVariable = null;
     console.log(emptyVariable);
 
 
@@ -59,9 +59,9 @@ myBoolean is equal to false
 
 Solution
 --------
-var myNumber=4;
-var myString="Variables are great.";
-var myBoolean=false;
+const myNumber=4;
+const myString="Variables are great.";
+const myBoolean=false;
 console.log("myNumber is equal to " + myNumber);
 console.log("myString is equal to " + myString);
 console.log("myBoolean is equal to " + myBoolean);