Not specific to developer tools, but definitely handy for using console.log etc: in JS, an expression can be any comma-separated set of expressions. Every sub-e

Not specific to developer tools, but definitely handy for using console.log etc: in JS, an expression can be any comma-separated set of expressions. Every sub-expression is evaluated, the last sub-expression’s value produces the value of the full expression. So for example: const add = (a, b) => ( a + b ); produces the same return value as: const add = (a, b) => ( console.log('adding', { a, b }), a + b ); The log call will be evaluated, producing the desired side effect, its return value (`undefined`) is ignored, and otherwise add behaves the same as before. This can save 100s of paper cuts where you might otherwise rewrite a function or some other expression into a block of statements—in the arrow function case requiring curly braces and a return statement. Caveats: - sometimes you need to wrap the expression in parentheses to avoid syntax errors - it does not work with debugger statements, which have no expression equivalent