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If deeper and deepest are assert.deepEqual()'s strict East Coast siblings with engineering backgrounds, only-shallow is their laid-back California cousin. only-shallow is a library for structurally comparing JavaScript objects. It supports recursive / cyclical data structures, is written to avoid try / catch / throw (for speed), and has no dependencies. It's not particularly strict about matching types. It's more of a duck squeezer.

It has some optimizations but stresses correctness over raw speed. Unlike deepest, it has no native dependencies, so you can use it, like, wherever.

If you install Ben Noordhuis's buffertools into a project using only-shallow, it will use that to speed up comparison of Buffers.

The core algorithm is based on those used by Node's assertion library and the implementation of cycle detection in isEqual in Underscore.js.

I like to think the documentation is pretty OK.

only-shallow has this name because I'm old.


npm install only-shallow


var deepEqual = require('only-shallow')
if (!deepEqual(obj1, obj2)) console.log("yay! diversity!");


Copied from the source, here are the details of only-shallow's algorithm:

  1. Use loose equality (==) only for value types (non-objects). This is the biggest difference between only-shallow and deeper / deepest. only-shallow cares more about shape and contents than type. This step will also catch functions, with the useful (default) property that only references to the same function are considered equal. 'Ware the halting problem!
  2. null is an object – a singleton value object, in fact – so if either is null, return a == b. For the purposes of only-shallow, loose testing of emptiness makes sense.
  3. Since the only way to make it this far is for a or b to be an object, if a or b is not an object, they're clearly not the same.
  4. It's much faster to compare dates by numeric value (.getTime()) than by lexical value.
  5. Compare RegExps by their components, not the objects themselves.
  6. The parts of an arguments list most people care about are the arguments themselves, not the callee, which you shouldn't be looking at anyway.
  7. Objects are more complex:
    1. Return true if a and b both have no properties.
    2. Ensure that a and b have the same number of own properties (which is what Object.keys() returns).
    3. Ensure that cyclical references don't blow up the stack.
    4. Ensure that all the key names match (faster).
    5. Ensure that all of the associated values match, recursively (slower).


ISC. Go nuts.

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