get a javascript function name

js-get-fn-name.js

function getFnName(fn) {
  fn = Object(fn)
  var F = typeof fn == 'function'
  var N = fn.name
  var S = F && ((N && ['', N]) || fn.toString().match(/function ([^\(]+)/))
  return (!F && 'not a function') || (S && S[1] || 'anonymous');
}

console.log(getFnName(String)); // 'String'
console.log(getFnName(function test(){})); // 'test'

console.log(getFnName(function (){})); // 'anonymous'
console.log(getFnName(function(){})); // 'anonymous'
console.log(getFnName(() => {})); // 'anonymous'

console.log(getFnName({ name: 'test' })); // 'not a function'
console.log(getFnName('test')); // 'not a function'
console.log(getFnName()) // 'not a function'
console.log(getFnName(null)) // 'not a function'

try {
  console.log(getFnName(Function())); // 'anonymous'
} catch(e) {
  console.error("eval() not supported")
}