ast-compare^4.2.1

Installation

Quick Take

Examples

• Compare Arrays
• Compare Plain Objects
• Compare Strings
• opts.arrayOrder
• opts.hungryForWhitespace
• opts.matchStrictly
• opts.useWildcards
• opts.verboseWhenMismatches
• Match each unordered array element only once
• Compare nested arrays without regard to order
• Match object keys using wildcards

Purpose

It compares data structures, especially, AST’s.

We use it to compare two parsed HTML/CSS trees or their branches, but you can compare anything, it will recursively traverse arrays too. For example, it powers ast-delete-object which also works on AST’s.

The default mode is similar to Tap asserts t.match and the option opts.matchStrictly is similar to t.sameStrict.

API — compare()

The main function compare() is imported like this:

It’s a function which takes three input arguments:

• If everything from smallObj matches everything within bigObj, this library returns true.
• Otherwise, if there’s a mismatch or something wrong with input args, it returns false.

None of the input arguments will be mutated by this program, we have unit tests to prove that.

The optional options object has the following shape:

The function returns a boolean:

A positive answer is always boolean true.

A negative answer is either:

• a boolean false (on default setting, if opts.verboseWhenMismatches is false) OR
• a string, explaining what didn’t match (if opts.verboseWhenMismatches is true)

API — defaults

You can import defaults:

It's a plain object:

The main function calculates the options to be used by merging the options you passed with these defaults.

API — version

You can import version:

API — types

This package is written in TypeScript and exports the following types:

import type { AnyObject, JsonArray, JsonObject, JsonValue, Opts } from "ast-compare";

opts.verboseWhenMismatches

Sometimes you just want a yes/no answer is something a subset or equal to something. But sometimes, the whole point of comparison is to inform the user exactly what is mismatching. In the latter cases, set opts.verboseWhenMismatches to true. When there is no match, instead of Boolean false the main function will return a string with an explanatory message.

If you use this setting, you have to anticipate Boolean true OR something else (Boolean false or string) coming out from this library.

Differences from _.isMatch

Partial comparisons will match empty array and empty object source values against any array or object value, respectively.

Lodash documentation

_.isMatch positively matches empty arrays to everything. This is bad when you are comparing parsed HTML/CSS trees. This library doesn’t do this. An empty array will not be reported as equal to a non-empty array.

// in this library:
var res = compare(["a", "b", "c"], []);
// now, res === false

Changelog