Hands-On Design Patterns with React Native

Referential transparency

Pure functions are referentially transparent, meaning that their function invocation can be replaced with its corresponding outcome for a given argument.

Now, look at the examples of referentially-transparent and referentially-opaque functions:

 let globalValue = 0;

 const inc1 = (num) => { // Referentially opaque (has side effects)
   globalValue += 1;
   return num + globalValue;
 }

 const inc2 = (num) => { // Referentially transparent
   return num + 1;
 }

Let's imagine a mathematical expression:

inc(4) + inc(4) * 5// With referentially transparent function you can simplify to:inc(4) * ( 1 + 1*5 )// and even toinc(4) * 6

Be aware that you need to avoid such simplifications if your function is not referentially transparent. ...