The ultimate guide to coding interviews: Learn and practice JavaScript design patterns tested by FAANG engineers. Get interview-ready in just a few hours with battle-tested solutions.

If you're an experienced developer, chances are your interviewer won't ask you about language syntax. Instead, they'll focus on things that test your understanding of software architecture, and how capable you are at finding optimized solutions to given problems. 

That’s where a strong understanding of design patterns comes in handy. It's often useful to be able to draw on established patterns instead of reinventing the wheel.

In this course, you will learn how to effectively deploy design patterns to answer interview questions. The course is divided into four sections: Creational Patterns, Structural Patterns, Behavioral Patterns, and Architectural Patterns. Each section has its own set of design patterns which you’ll learn to use through various challenges. 

Every challenge contains a detailed solution explanation. By the end of this course (and with some practice), you will be able to confidently use design patterns to tackle advanced coding interview questions in JavaScript.

JavaScript Design Patterns for Coding Interviews

## Explanation


In the solution, the first line defines the variable `configure` which stores the reference to the first instance of `ConfigureVals`. This variable is only initialized once. 

The `constructor` of the class accepts the object parameter `initvalues`. It defines and initializes the values `xpoint`, `ypoint`, and `shape` from **lines 4-6**.

```
this.xpoint = initvalues.xpoint || 0;
this.ypoint = initvalues.ypoint || 0;
this.shape = initvalues.shape || null;
```

As mentioned in the challenge, if no value of either `xpoint`, `ypoint`, or `shape` is given, the values are set to `0`, `0`, `null`.

The class contains the `getConfiguration` method, which accepts the object parameter `initvalues`. In **line 9**, the `if` condition checks whether an instance for the class already exists.

```
if (!configure)
```

If it does not, a new instance is created (**line 10**).

```
configure = new ConfigureVals(initvalues)
```

If an instance already exists, it is returned (**line 12**). Hence, no new instance is created.

```
return configure;
```

In line 16, a new instance is created.

```
var configureObj1 = ConfigureVals.getConfiguration({ "xpoint": 8, "ypoint" : 9, "shape" : "rectangle" });
```

Since this is the first instance it is created,  you will see the following output:

```
ConfigureVals { xpoint: 8, ypoint: 9, shape: 'rectangle' }
```

In line 18, the `getConfiguration` method is called again. 

```
var configureObj2 = ConfigureVals.getConfiguration({ "xpoint": 2, "ypoint": 4, "shape" : "circle" });

```

However, since an instance already exists, the first instance is returned. Hence, you see the following output:

```
ConfigureVals { xpoint: 8, ypoint: 9, shape: 'rectangle' }
```

So, both `configureObj1` and `configureObj2` are the same.

# Explanation


In the solution, the first line defines the variable `configure` which stores the reference to the first instance of `ConfigureVals`. This variable is only initialized once. 

The `constructor` of the class accepts the object parameter `initvalues`. It defines and initializes the values `xpoint`, `ypoint`, and `shape` from **lines 4-6**.

```
this.xpoint = initvalues.xpoint || 0;
this.ypoint = initvalues.ypoint || 0;
this.shape = initvalues.shape || null;
```

As mentioned in the challenge, if no value of either `xpoint`, `ypoint`, or `shape` is given, the values are set to `0`, `0`, `null`.

The class contains the `getConfiguration` method, which accepts the object parameter `initvalues`. In **line 9**, the `if` condition checks whether an instance for the class already exists.

```
if (!configure)
```

If it does not, a new instance is created (**line 10**).

```
configure = new ConfigureVals(initvalues)
```

If an instance already exists, it is returned (**line 12**). Hence, no new instance is created.

```
return configure;
```

In line 16, a new instance is created.

```
var configureObj1 = ConfigureVals.getConfiguration({ "xpoint": 8, "ypoint" : 9, "shape" : "rectangle" });
```

Since this is the first instance it is created,  you will see the following output:

```
ConfigureVals { xpoint: 8, ypoint: 9, shape: 'rectangle' }
```

In line 18, the `getConfiguration` method is called again. 

```
var configureObj2 = ConfigureVals.getConfiguration({ "xpoint": 2, "ypoint": 4, "shape" : "circle" });

```

However, since an instance already exists, the first instance is returned. Hence, you see the following output:

```
ConfigureVals { xpoint: 8, ypoint: 9, shape: 'rectangle' }
```

So, both `configureObj1` and `configureObj2` are the same.

This lesson will explain the solution to the problem from the previous coding challenge.


Before We Begin

Introduction To Design Patterns

Creational Patterns

Structural Patterns

Behavioral Patterns

Architectural Patterns

Conclusion

Challenge: Solution Review

Solution #

Explanation