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Is there a way to set the default attribute of a Javascript object such that:
let emptyObj = {}; // do some magic emptyObj.nonExistingAttribute // => defaultValue 
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In JavaScript, function parameters default to undefined . However, it's often useful to set a different default value. This is where default parameters can help. In the past, the general strategy for setting defaults was to test parameter values in the function body and assign a value if they are undefined .
The OR Assignment (||=) Operator The logical OR assignment ( ||= ) operator assigns the new values only if the left operand is falsy. Below is an example of using ||= on a variable holding undefined . Next is an example of assigning a new value on a variable containing an empty string.
To change the value of an existing property of an object, specify the object name followed by: a dot, the name of the property you wish to change, an equals sign, and the new value you wish to assign.
Objects. Variables of any "Object" type (which includes all the classes you will write) have a default value of null.
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 Read more in Mozilla's documentation on Proxies.
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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.
var emptyObj = {}; const { nonExistingAttribute = defaultValue } = emptyObj; console.log(nonExistingAttribute); // defaultValue 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 If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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