Set default value of Javascript object attributes

Question

Is there a way to set the default attribute of a Javascript object such that:

let emptyObj = {}; // do some magic emptyObj.nonExistingAttribute // => defaultValue 

Answer 1

Since I asked the question several years ago things have progressed nicely.

Proxies are part of ES6. The following example works in Chrome, Firefox, Safari and Edge:

let handler = {   get: function(target, name) {     return target.hasOwnProperty(name) ? target[name] : 42;   } };  let emptyObj = {}; let p = new Proxy(emptyObj, handler);  p.answerToTheUltimateQuestionOfLife; //=> 42 

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Read more in Mozilla's documentation on Proxies.

Answer 2

Use destructuring (new in ES6)

There is great documentation by Mozila as well as a fantastic blog post that explains the syntax better than I can.

To Answer Your Question

var emptyObj = {}; const { nonExistingAttribute = defaultValue } = emptyObj; console.log(nonExistingAttribute); // defaultValue 

Going Further

Can I rename this variable? Sure!

const { nonExistingAttribute: coolerName = 15} = emptyObj; console.log(coolerName); // 15 

What about nested data? Bring it on!

var nestedData = {     name: 'Awesome Programmer',     languages: [         {             name: 'javascript',             proficiency: 4,         }     ],     country: 'Canada', };  var {name: realName, languages: [{name: languageName}]} = nestedData ;  console.log(realName); // Awesome Programmer console.log(languageName); // javascript