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POJavascript: what are some guidelines on how to define new data types?
 

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    <p>Suppose you are creating the data type and expose its behavior. </p> <p>Can you give some examples of when would you use:</p> <ul> <li><p>a function &amp; new:</p> <pre><code>// define new data type var CustomDataType= function(){ this.a='whatever'; this.doX= function(){/*some code*/}; } // create a new instance of our custom data type var obj= new customDataType(); </code></pre></li> <li><p>an object literal &amp; Object.create:</p> <pre><code>// define new data type var customDataType = { a: 'whatever', doX: function(){/*some code*/} } // create a new instance of our custom data type var obj= Object.create(customDataType); </code></pre></li> <li><p>a function that builds your object:</p> <pre><code>function customDataTypeFactory(options){ return { a: 'whatever', doX: function(){/*some code*/} } }; // create a new instance of our custom data type var obj= customDataTypeFactory(options); </code></pre></li> </ul> <p>I feel this could be labeled duplicate for: <code>new</code> vs <code>Object.create</code> but my main interest is not in discussing which one is better but rather to know if there are specific use cases where one should be preferred over the others.</p> <p>I have read many posts on related questions and the book from Crockford: Javascript: the good parts. So far I have concluded that it is a matter of preference, tough the advice from Crockford resonates a lot with me to me: "try to avoid the features that are dangerous and unnecessary"... I'm talking about <code>new</code>.</p>
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    1. COYour first and third versions put properties directly on the new object. In your second version, the object inherits the properties. I don't know that there's any concrete answer to your question. The first one uses a constructor if you invoke using `new`, and `instanceof` will work to identify that object. The third one doesn't require the use of `new`, but `instanceof` won't be as useful. The second one again inherits the properties, so building several objects that way will all share the data, and all the objects will observe updates to the inherited object.
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    2. CO...and don't get too hung up on Crockford's danger warnings. I think he worries a little too much. I mean, take it all in, but take it with a grain of salt.
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    3. CO`this.doX=` should be `doX :` in the last two snippets
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