Code Smell 155 - Multiple Promises

You have promises. You need to wait. Wait for them all

TL;DR: Don't block yourself in a sorted way.

Problems

• Indeterminism
• Performance bottleneck

Solutions

1. Wait for all promises at once.

Context

We heard about semaphores while studying Operating Systems.

We should wait until all conditions are met no matter the ordering.

Sample Code

Wrong

async fetchOne() { /* long task */ }
async fetchTwo() { /* another long task */ }

async fetchAll() {
  let res1 = await this.fetchOne(); 
  let res2 = await this.fetchTwo();
  // they can run in parallel !!  
}
        

Right

async fetchOne() { /* long task */ }
async fetchTwo() { /* another long task */ }

async fetchAll() {
  let [res3, res4] = await Promise.all([this.fetchOne(), this.fetchTwo()]);
  //We wait until ALL are done
}        

Detection

[X] Semi-Automatic

This is a semantic smell.

We can tell our linters to find some patterns related to promises waiting.

Tags

• Performance

Conclusion

We need to be as close as possible to [real-world]((https://www.dhirubhai.net/pulse/what-wrong-software-maximiliano-contieri/) business rules.

If the rule states we need to wait for ALL operations, we should not force a particular order.

Credits

Thanks for the idea

Twitter

Photo by?Alvin Mahmudov?on?Unsplash

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This article is part of the CodeSmell Series.

How to Find the Stinky parts of your Code