fleg/tcompare

A comprehensive comparison library, for use in test frameworks

tcompare

A comprehensive comparison library, for use in test frameworks. Walks an object once, generating both a simple true/false result, as well as a nicely formatted human-readable diff string.

USAGE

const { match, same, strict, has, hasStrict, format } = require('tcompare')

// Result is an object with { Boolean match, String diff }
const result = match(object, pattern)
if (!result.match) {
  console.log(`item did not match pattern`)
  console.log(result.diff)
} else {
  console.log(`it's a match!`)
}

METHODS

• format(object, [options]) - No comparisons performed. Just print out the object. Returns just the string format.
• same(object, pattern, [options]) - Ensure that all items in the pattern are found in the object, and vice versa, matching loosely (so, for example 1 will match with '1').
• strict(object, pattern, [options]) - Ensure that all items in the pattern are found in the object, and vice versa, matching strictly (so, for example 1 will not match with '1').
• has(object, pattern, [options]) - Ensure that all items in the pattern are found in the object, but ignore additional items found in the object, matching loosely.
• hasStrict(object, pattern, [options]) - Ensure that all items in the pattern are found in the object, but ignore additional items found in the object, matching strictly.
• match(object, pattern, [options]) - Verify that all items in pattern are found in object, and that they match. This is the loosest possible algorithm, allowing cases where we just want to verify that an object contains a few important properties. The algorithm is the same as the one used by tmatch. In a nutshell:
  • If the object and pattern are loosely equal, then pass
  • If the object and the pattern are both Regular Expressions, Date objects or Buffers, then pass if they're "equivalent".
  • If the pattern is a RegExp, cast object to a string, and test against the RegExp.
  • If both are Strings, pass if pattern appears in object.
  • If pattern is a function, and object is an instance of that function, then pass. (This also applies to Symbol, Number, String, etc.)
  • If pattern and object are collections (object, map, set, array or iterable), then compare their contents. Each type of collection can only match its same type, with the exception of non-Set iterables (including arguments objects), which are cast to Arrays.

There are classes exported to correspond to each of these. All of these are instantiated like new Format(object, options). An expect option is required for all classes except Format. Call obj.print() on the resulting object to generate a diff. Once the diff (or format) is generated, it'll have a match boolean member.

OPTIONS

Each method can take the following options.

• includeEnumerable - Set to true to walk over all enumerable properties of a given object when comparing or formatting, rather than the default of only showing enumerable own-properties. Note that calling getter functions may be hazardous, as they may trigger side-effects.

• includeGetters - Set to true to walk over all enumerable getters on an object's prototype (but not from further down the prototype chain), in addition to own-properties. This is useful in cases where you want to compare or print an object with enumerable getters that return internal values in a read-only manner. Note that calling getter functions can be hazardous, as they may trigger side-effects.

• sort - Set to true to sort object keys. This is important when serializing in a deterministic way.

• style - Set to pretty for a very human-readable style of object printing. Set to js for a copy-and-paste friendly valid JavaScript output. Set to tight for a minimal white-space js format. Default is pretty. Example:

  // pretty style
  Object {
    "myMap": Map {
      Object {
        "a": 1,
      } => Object {
        "b": 2,
      }
    }
  }
  
  // js style
  {
    "myMap": new Map([
      [{
        "a": 1,
      }, {
        "b": 2,
      }]
    ])
  }
  
  // tight style
  {"myMap":new Map([[{"a":1,},{"b":2,}],]),}
  

  Note that tight is not suitable for comparisons, only formatting.

Circular References

Circular references are displayed using YAML-like references, so it's easy to determine which item is circularly referenced.

When doing comparisons, a pattern and object will be considered matching if they contain the same circularity. So, for example, if a pattern refers to itself, then an object should refer to itself as well.

const a = {list: [], b: {}}
a.list.push(a)
a.list.push(a.b)
a.b.a = a
console.log(format(a))

/*
&ref_1 Object {
  "list": Array [
    <*ref_1>,
    Object {
      "a": <*ref_1>,
    },
  ],
  "b": Object {
    "a": <*ref_1>,
  },
}
*/

Note that circular references are never going to be valid JavaScript, even when using the js style.