Update 03_default_function_arguments.md

Improve syntax highlighting code

Author: Sam Zeng

ebook/03_default_function_arguments.md

@@ -2,7 +2,7 @@
 
 Prior to ES6, setting default values to function arguments was not so easy. Let's look at an example:
 
-```js
+``` js
 function getLocation(city,country,continent){
   if(typeof country === 'undefined'){
     country = 'Italy'
@@ -26,7 +26,7 @@ When calling `getLocation('Milan')` the second and third parameter (country and
 
 But what if we want our default value to be at the beginning and not at the end of our list of arguments?
 
-```js
+``` js
 function getLocation(continent,country,city){
   if(typeof country === 'undefined'){
     country = 'Italy'
@@ -39,6 +39,7 @@ function getLocation(continent,country,city){
 
 getLocation(undefined, undefined,'Milan')
 // Europe Italy Milan
+
 getLocation(undefined,'Paris','France')
 // Europe Paris France
 ```
@@ -51,7 +52,7 @@ If we want to replace any of the first arguments with our default we need to pas
 
 ES6 makes it very easy to set default function arguments. Let's look at an example:
 
-``` javascript
+``` js
 function calculatePrice(total, tax = 0.1, tip = 0.05){
 // When no value is given for tax or tip, the default 0.1 and 0.05 will be used
 return total + (total * tax) + (total * tip);
@@ -60,14 +61,14 @@ return total + (total * tax) + (total * tip);
 
 What if we don't want to pass the parameter at all, like this:
 
-``` javascript
+``` js
 // The 0.15 will be bound to the second argument, tax even if in our intention it was to set 0.15 as the tip
 calculatePrice(100, 0.15)
 ```
 
 We can solve by doing this:
 
-``` javascript
+``` js
 // In this case 0.15 will be bound to the tip
 calculatePrice(100, undefined, 0.15)
 ```
@@ -76,7 +77,7 @@ It works, but it's not very nice, how to improve it?
 
 With **destructuring** we can write this:
 
-``` javascript
+``` js
 function calculatePrice({
   total = 0,
   tax = 0.1,
@@ -86,7 +87,6 @@ function calculatePrice({
 
 const bill = calculatePrice({ tip: 0.15, total:150 });
 // 187.5
-```
 
 const bill = calculatePrice({ tip: 0.15, total:150 });
 // 187.5
@@ -98,22 +98,23 @@ In the example above the default value for *tip* was 0.05 and we overwrote it wi
 
 Notice this detail:
 
-```js
+``` js
 {
   total = 0,
   tax = 0.1,
-  tip = 0.05} = {}
+  tip = 0.05
+} = {}
 ```
 
 If we don't default our argument Object to an empty Object, and we were to try and run `calculatePrice()` we would get:
 
-```js
+``` javascript
 Cannot destructure property `total` of 'undefined' or 'null'.
 ```
 
 By writing ` = {}` we default our argument to an `Object` and no matter what argument we pass in the function, it will be an `Object`:
 
-```js
+``` js
 calculatePrice({});
 // 0
 calculatePrice();
@@ -128,17 +129,18 @@ Don't worry about destructuring, we will talk about it in Chapter 10.
 
 Note: We now don't need to construct object and equate to an empty object. Alternative to above we can construct a function as below
 
-``` javascript
+``` js
 function calculatePrice({
   total = 0,
   tax = 0.1,
   tip = 0.05}){
   return total + (total * tax) + (total * tip);
-}```
+}
+```
 
 and the below code would work normal
 
-```js
+``` js
 calculatePrice({});
 // 0
 calculatePrice();