testing the order of properties in javascript objects

"use strict"; // Experiment - testing the order of properties in Objects let obj1 = {c: 'Fred', a: 'Hi', b: 'There'}; // non-numeric keys let obj2 = {100: 'Fred', 200: 'Hi', 300: 'There'}; // numeric-keys in ascending order let obj3 = {'100': 'Fred', '2': 'Hi', '7': 'There'}; // (quoted) numeric-keys in non-ascending order // test order of properties console.log(Object.getOwnPropertyNames(obj1)); // [ 'c', 'a', 'b' ] (insertion order) console.log(Object.getOwnPropertyNames(obj2)); // [ '100', '200', '300' ] (ascending) console.log(Object.getOwnPropertyNames(obj3)); // [ '2', '7', '100' ] (ascending) // translate objects into arrays: let arr1 = Object.keys(obj1).map(key => obj1[key]); let arr2 = Object.keys(obj2).map(key => obj2[key]); let arr3 = Object.keys(obj3).map(key => obj3[key]); console.log(arr1); // [ 'Fred', 'Hi', 'There' ] console.log(arr2); // [ 'Fred', 'Hi', 'There' ] console.log(arr3); // [ 'Hi', 'There', 'Fred' ] // for ... in loops for (let item in obj1) { console.log(item); } for (let item in obj2) { console.log(item); } for (let item in obj3) { console.log(item); } // Tested on Node, Edge, Chrome, IE11, Firefox // Not tested: Safari // verdict: there is no guarantee in the ECMA spec (ecma-262) about the order of object properties. // However, in Practice: // Firefox, Node, Edge, Chrome, IE11: // properties with non-numeric keys are iterated in the order they were inserted, // properties with numeric keys are sorted in ascending order (this includes "stringified" numbers eg "100" or '100') // // more info here: https://bugs.chromium.org/p/v8/issues/detail?id=164