React: expected an assignment or function call and instead saw an expression no-unused-expressions

The issue got solved by adding this to the top of the file:

/* eslint-disable */

Obviously the expression causing the issue. But looking at your expression, I think you want to do simply like:

a[m] = f || []

Instead of:

 var f = a[m];
      f || (f = [], a[m] = f);

Anyways, allowShortCircuit should solve your issue:

/*eslint no-unused-expressions: [
  "error", { 
    "allowShortCircuit": true
  }]*/

For further configuration, see:

no unused expression

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