20 July 2021

Why you should care

While most script engines support Function Declarations within blocks it is not part of ECMAScript (see ECMA-262, clause 13 and 14). Worse implementations are inconsistent with each other and with future EcmaScript proposals. ECMAScript only allows for Function Declarations in the root statement list of a script or function. Instead use a variable initialized with a Function Expression to define a function within a block.

How we detect

This Code Insight counts one occurrence each time a function is declared in a block:

Bad Code

if (x) {
function foo() {}
}

Good Code

function bar() {
  function inner() {return i;}
  if (x) {
     var foo = function() {}; 
   }
}

References

https://stackoverflow.com/questions/15663098/function-declarations-should-not-be-placed-in-blocks
https://rules.sonarsource.com/javascript/RSPEC-1530

About CAST and Highlight’s Code Insights

Over the last 25 years, CAST has leveraged unique knowledge on software quality measurement by analyzing thousands of applications and billions of lines of code. Based on this experience and community standards on programming best practices, Highlight implements hundreds of code insights across 15+ technologies to calculate health factors of a software.

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