による

Caused by/Done by/Depends on
Noun + による/によって

による is a phrase that means “to be caused by”, “determined by”, or “performed by”.
Typically It identifies the cause or source of something. 
It is most similar to で, and can be replaced by it in most cases.
による (Noun modification)、によって (Standard)、or により (Typically written only). 

Due to

The most common usage of による is to mark the cause or source of something, same as で

Examples

• 台風の影響による大雨警報が解除されました
  The rain warning caused by the typhoon has been canceled.
  
  
• コロナによって欠席した人が多い。
  There are a lot of people absent due to Corona.
  
  
• 大雪により、学校は休みとなりました。
  As a result of the snow, school was canceled.
  
  
• 事件の影響により、新し制度が作られた
  As a result of the influence of that incident, a new system was created.
  
  
• 怪我によって参加できなかった
  Unable to participate due to an injury.
  
  

Performed by

In some cases, による means “performed by” (Source of something). Same as で.
I listed this separately, but a lot of times it blurs into the “caused by” meaning.

Examples

• BBCによる独占テレビインタビュー (Weblio)
  An exclusive interview by the BBC. 
  
  
• 彼によるパフォーマンス
  A performance by him.
  
  
• 怒りによっての発言
  Something spoken “by” anger. (Yes this is also “due to”)
  
  
• 科学者たちによる植物の新種の発見 (Weblio)
  The discovery of a new species of plant by scientists.
  
  

Depending on/Determined by

One more usage of による is to communicate “depends on”. Also same as で.
This is typically used with a word like 違う、ことなる、決める, etc.
The most typically phrase involving this is: 人によって – Depending on the person.
This meaning is most similar to しだい (page not yet made)

Examples

• 人によって考え方はちがう
  Ways of thinking are different depending on the person.
  
  
• 社長の判断によってこれからの方策を決める
  Our policy going forward will be determined by the CEO’s decision.
  
  
• 結果によって合格か不合格が決まる
  The result will determine whether you pass or fail.
  
  
• 彼の気分によって君の運命が決まる
   Your fate depends on his mood. 

によっては

によっては has the same meaning as によって, but uses contrastive は.
Because this is contrastive は, this means that any statement should also have an opposite statement;
I.E. This pattern should be used for dichotomous sentences. If you can’t say “Or not” after it, you probably can’t use によっては

Examples

• 国によっては18歳で酒を飲むことができる
  Depending on the country, you can drink at 18 (others you can’t). 
  
  
• 材料によって味が変わる
  The taste changes depending on the ingredients. (よっては is weird).
  
  
• 材料によっては美味しい.
  Depending on the ingredients, it will taste good. (Or not).  
  
  
• 働きによっては賞与がもらえる
  Depending on your effort, you may get a bonus. 
  
  
• 働きによって賞与が決まる
  Your bonus will be based on your effort. 
  
  

Reference