# Code Smell 222 - Comma Operator

> TL;DR: Use comma operator just for loops

# Problems

- Readability

- Hidden Defects

# Solutions

1. Avoid operator usage

2. Prefer *[foreach](https://maximilianocontieri.com/code-smell-53-explicit-iteration)* operator

3. Break the sentences

# Context

In JavaScript, the comma operator allows you to evaluate multiple expressions sequentially and return the value of the last expression.

It's denoted by a comma and separates multiple expressions within a larger expression.

Each expression is evaluated in order from left to right, and the final value of the entire comma-separated expression is the value of the last expression.

# Sample Code

## Wrong

[Gist Url]: # (https://gist.github.com/mcsee/b18abdb155a811f6f3f694b079837330)
```javascript
const gravitationalConstant = 6.67430e-11;

const massBlackHole1 = 1.5e31;  // Mass of the first black hole in kg
const massBlackHole2 = 2.2e32;  // Mass of the second black hole in kg
const distanceBlackHoles = 5.7e20;  // Distance between black holes in meters

var force = (distanceSquared = distanceBlackHoles * distanceBlackHoles,
             (gravitationalConstant * massBlackHole1 * massBlackHole2) /
             distanceSquared);

// Two operations in a single statement with comma operator     

console.log("Gravitational force between two black holes:", force);
```

## Right

[Gist Url]: # (https://gist.github.com/mcsee/3a928ca6aa06e70c0f20d40487c6bad9)
```javascript
function calculateGravitationalForce(mass1, mass2, distance) {
  const gravitationalConstant = 6.67430e-11;
  return (gravitationalConstant * mass1 * mass2) / (distance * distance);  
}

const massBlackHole1 = 1.5e31;  // Mass of the first black hole in kg
const massBlackHole2 = 2.2e32;  // Mass of the second black hole in kg
const distanceBlackHoles = 5.7e20;  // Distance between black holes in meters

const force = calculateGravitationalForce(
  massBlackHole1,
  massBlackHole2,
  distanceBlackHoles
);

// Notice force is calculated with a separate function

console.log("Gravitational force between two black holes:", force);

```

# Detection

[X] Automatic 

Many [linters](https://rules.sonarsource.com/javascript/RSPEC-878/) can detect this problem.

# Exceptions

- For loops are a valid exception dough they might lead you to [another code smell](https://maximilianocontieri.com/code-smell-53-explicit-iteration)

# Tags

- Readability

# Conclusion

This valid operator was designed to shorten *for loops* but is now sometimes abused.

# Relations

%[https://maximilianocontieri.com/code-smell-53-explicit-iteration]

# Disclaimer

Code Smells are my [opinion](https://maximilianocontieri.com/i-wrote-more-than-90-articles-on-2021-here-is-what-i-learned).

# Credits
Photo by [Stephen Hickman](https://unsplash.com/@stevo6960) on [Unsplash](https://unsplash.com/photos/YmNrPi4FfLU)
    
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> My computer's so fast it finishes an infinite loop in 5 minutes.

_Chisel Wright_
 
%[https://maximilianocontieri.com/software-engineering-great-quotes]

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This article is part of the CodeSmell Series.

%[https://maximilianocontieri.com/how-to-find-the-stinky-parts-of-your-code]