javascript - How to Test an optional member of an object? -

what best technique test optional object member. right prefacing expect statements if:

 if(object.member) expect(object).to.have.a.property('member').that.is.a('string'); 

but there must method more inline stylistically. e.g.

 expect(object).to.have.an.optional.property('member').that.is.a('string'); 

or (adding empty chain, readability):

 expect(object).to.have.an.optional.property('member').that.would.be.a('string'); 

or (moving optional provide alternative version of expect):

 optionally.expect(object).to.have.a.property('member').that.is.a('string'); 

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update - started write code (new chai) see if accomplish targeting, added small plugin:

module.exports = function(chai, utils) {     var assertion = chai.assertion         , = utils.inspect         , flag = utils.flag;      var optional_flag = 'chai-optional/option'     assertion.addproperty('optional', function() {         flag(this, optional_flag, true)         return this;     })      assertion.overwritemethod('property', function (_super) {         return function assertproperty (propertyname) {             if (flag(this, optional_flag)) {                 flag(this, optional_flag, false) ;                  var obj = this._obj;                 var ispropertypresent = (obj[propertyname]) ? true : false ;                  if(ispropertypresent) {                     return _super.apply(this, arguments);                 }              } else {                 _super.apply(this, arguments);             }         };     });      assertion.addproperty('would', function () {         return this;     }); }; 

with usage:

it('could null or have value', function(done){     var objwithout = {}     var objwith = {}     objwith.someproperty = 'blah'      expect(objwith).to.have.optional.property('someproperty').that.would.be.a('string');     expect(objwithout).to.have.optional.property('someproperty').that.would.be.a('string');      return done(); }) 

the current problem when property isn't present, control of function ends - evaluation chain continues. need end evaluation out failing assertion - possible?

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update either solution (simplistic solution):

var either = function(firstcondition){     var returnobject = {}      try{         firstcondition()         returnobject.or = function(secondcondition){ return }     } catch(e) {         returnobject.or = function(secondcondition){ return secondcondition() }     }     return returnobject ; }  module.exports = either 

i think implementation little clunky - fat arrow functions hap thin out of syntax. here waiting on that!

the current problem when property isn't present, control of function ends - evaluation chain continues. need end evaluation out failing assertion - possible?

after having read chai's plugin guide have used similar approach flag. however, have reached same conclusion - cannot stop chain.

a possibility though of not implement new properties , new flag, overwrite assert method - not throw when optional_flag flag on current assertion object set. however, chance destroy or miss edge case hight.

after all, don't think it's idea. citing this "confusing syntax" issue:

i think misunderstanding comes expectation chai follows most/all english grammar rules. unfortunately, english grammar has way many rules (and exceptions rules) reasonable undertaking implement.

the challenge designing chai's chain-able assertions finding balance between being expressive , concise. if full grammar wasn't daunting task implement , document, make api less concise, not testing environment.

rule: "flag" modifies behavior of assertion (negation not or inclusion include/contain , etc...), once set true should remain true until end of chain.

this means impossible implement .or operator well.

what possible though implement like

either(function(){     expect(object).not.to.have.a.property('member'); }).or(function(){     expect(object).to.have.a.property('member').that.is.a('string'); }); 

maybe 1 can build more appealing syntax on that.