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POModify a global variable based on an object property
 

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    <p>I'm trying to learn object oriented javascript and ran into the following problem:</p> <p>I have an object constructor (is that the right term?) like this:</p> <pre><code>function itemCreator(itemName, itemType, itemPositionX, itemPositionY) { this.itemName = itemName; this.itemType = itemType; this.itemPositionX = itemPositionX; this.itemPositionY = itemPositionY; allItems.push(this); //store all items in a global variable }//end itemCreator; //then I use it to create an object megaRocket = new itemCreator ( 'megarocket', 'item_megarocket', 108, 475 ) </code></pre> <p>Now I realised I also need to map these objects to modify different global variables based on which "itemType" the object has. This is where I am stuck. How can I make a global variable that only objects with a specific itemType property can modify?</p> <p>For example I would like to create an object that increments a variable called amountOfMegarockets, but only if the itemType for that object is "item_megarocket".</p> <p>I later plan on looping an array of these items to see if player object touches them (to collect the item):</p> <pre><code>function checkForItems(){ var itemLen =allItems.length; for (i=0; i &lt; itemLen; i++){ var itemObject = allItems[i]; if ( //checking for "collisions" here (ship.x &lt; (itemObject.itemBitmap.x + itemObject.size) &amp;&amp; (ship.x + shipWidth) &gt; itemObject.itemBitmap.x) &amp;&amp; (ship.y &lt; (itemObject.itemBitmap.y + itemObject.size) &amp;&amp; (ship.y + shipWidth) &gt; itemObject.itemBitmap.y) ){ itemObject.actor.y = -500; //just removing the item from canvas here (temporary solution) // Here comes pseudo code for the part that I'm stuck with variableBasedOnItemObject.itemType++; } </code></pre> <p>I hope my explanation makes sense to someone!</p> <p>EDIT:</p> <p>Bergi's answer makes most sense to me, but I can't get the syntax right. Here's how I'm trying to use Bergi's code:</p> <pre><code>var amounts = {}, allItems = []; function itemCreator(itemName, itemType, itemPositionX, itemPositionY) { this.itemName = itemName; this.itemType = itemType; this.itemPositionX = itemPositionX; this.itemPositionY = itemPositionY; (amounts[itemType]=2); // this is different from bergi's example because I need to set the initial value of the item to two //I also shouldn't increase the item amount on creation of the item, but only when it's specifically called from another function this.increaseCount = amounts[itemType]++; //this should IMO increase the itemType amount inside the amounts object when called, but it doesn't seem to work } //creating the object the way bergi suggested: allItems.push(new itemCreator('shootUp001', 'item_up', 108, 475)); </code></pre> <p>Now here's the problematic part:</p> <pre><code>function checkForItems(){ var itemLen =allItems.length; for (i=0; i &lt; itemLen; i++){ var itemObject = allItems[i]; if ( my condition here) ){ //code below is not increasing the value for the current itemType in the amounts object. //Probably a simple syntax mistake? itemObject.itemType.increaseCount; } } } </code></pre> <p>Why is my call of itemObject.itemType.increaseCount; not increasing the value of amounts.itemType?</p>
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    1. COIMO, this isn't the right approach at all. You should separate your logic into different classes, not under one monolithic class.
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    2. COIt's not a monolith class IMO, because all the "items" are very similar and share the same properties. The only main difference between different items should be the counter variable they affect.
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    3. COAny question starting with "modify global variable" is already asking the wrong question.
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      1. USIngo Bürk
 

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