JavaScript: isPrimitive

isprimitive-no-strict.js

var isPrimitive = function(val) {
  return val !== function() { return this; }.call(val);
};

isprimitive.js

'use strict';

var isPrimitive = function(val) {
  return val == null || /^[sbn]/.test(typeof val);
};

isprimitive_test.js

var assert = require('assert');

assert.ok(isPrimitive(null));
assert.ok(isPrimitive(undefined));
assert.ok(isPrimitive(1));
assert.ok(isPrimitive('foo'));
assert.ok(isPrimitive(true));
assert.ok(isPrimitive(false));
assert.ok(isPrimitive(NaN));
assert.ok(isPrimitive(Infinity));

assert.equal(isPrimitive({}), false);
assert.equal(isPrimitive([]), false);
assert.equal(isPrimitive(/./), false);
assert.equal(isPrimitive(global), false);
assert.equal(isPrimitive(function() {}), false);
assert.equal(isPrimitive(new function() {}), false);
assert.equal(isPrimitive(new Number), false);
assert.equal(isPrimitive(new String), false);
assert.equal(isPrimitive(new Boolean), false);
assert.equal(isPrimitive(new Date), false);
assert.equal(isPrimitive(new Error), false);
assert.equal(isPrimitive(Object.create(null)), false);
3

Regexp?

RegExp is represented via /./

function isPrimitive(val) {
return val !== Object(val);
}

function isPrimitive(val) {
return !Object.prototype.isPrototypeOf(val);
}

@AutoSponge, your second version of isPrimitive fails on objects created via Object.create(null, ....