JavaScript Numeric Separator test cases

numeric-separator-tests.js

// 11 Oct 2020

// tl;dr
// Numeric separators are parsed on numbers, not on string arguments passed to the Number constructor.
// JSON.stringify({ value: NaN }) returns "{"value":null}".

/* Test it out */

var tests = [
  1111222333,
  1_111_222_333,
  1.111_222_333,
  1.1_1_1_2_2_2_3_3_3,
  1.111_222_333e7,
  1.1_1_1_2_2_2_3_3_3e7,
  
  // The unformatted numeric string works.
  "1222333444",
  
  // Formatted strings don't, including coercion.
  "1_222_333_444", // null
  "1.2_2_2_3_3_3_4_4_4",  // null
  "1.2_2_2_3_3_3_4_4_4e7", // null
  +"1_333_444_555" // null
  
  // These result in parsing errors.
// 1.2__3, // SyntaxError: Only one underscore is allowed as numeric separator
// 1._1_1_1_2_2_2_3_3_3, // SyntaxError: Invalid or unexpected token 
// "1._2_2_2_3_3_3_4_4_4" // SyntaxError: Invalid or unexpected token  
];

var test = function(value) {
  var result;
  try { result = Number(value) }
  catch (error) { result = error }
  return result;
}

var results = tests.map((v, i) => {
  console.log(`test ${ i + 1 }:`, v );
  
  return { test: v, result: test(v) };
});

/*
  test 1: 1111222333
  test 2: 1111222333
  test 3: 1.111222333
  test 4: 1.111222333
  test 5: 11112223.33
  test 6: 11112223.33
  test 7: 1222333444
  test 8: 1_222_333_444
  test 9: 1.2_2_2_3_3_3_4_4_4
  test 10: 1.2_2_2_3_3_3_4_4_4e7
  test 11: NaN
*/

console.log(
  "Results:\n",
  JSON.stringify(results, null, 2)
);

/*
Results:
 [
  {
    "test": 1111222333,
    "result": 1111222333
  },
  {
    "test": 1111222333,
    "result": 1111222333
  },
  {
    "test": 1.111222333,
    "result": 1.111222333
  },
  {
    "test": 1.111222333,
    "result": 1.111222333
  },
  {
    "test": 11112223.33,
    "result": 11112223.33
  },
  {
    "test": 11112223.33,
    "result": 11112223.33
  },
  {
    "test": "1222333444",
    "result": 1222333444
  },
  {
    "test": "1_222_333_444",
    "result": null
  },
  {
    "test": "1.2_2_2_3_3_3_4_4_4",
    "result": null
  },
  {
    "test": "1.2_2_2_3_3_3_4_4_4e7",
    "result": null
  },
  {
    "test": null,
    "result": null
  }
]
*/

// The last result is curious. `+"1_333_444_555"` is reported as `null` in the stringified JSON.
// What about raw?

console.log( +"1_333_444_555" );
// NaN