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    <pre><code>var elements = [ { a:"a", b:"b"}, {a:"c", b:"d"}, {a:"e", b:"f"} ]; function getter(list, num) { var i, agg = { a: "", b: "" }; for (i = 0; i &lt;= num; i += 1) { agg.a += list[i].a; } return agg; } console.log(getter(elements, 0).a); // "a" console.log(getter(elements, 1).a); // "ac" console.log(getter(elements, 2).a); // "ace" </code></pre> <p>You can use a closure so you can't access the values, like:</p> <pre><code>var elements = [ { a:"a", b:"b"}, {a:"c", b:"d"}, {a:"e", b:"f"} ]; function make_getter(list) { return { get: function (num) { var i, agg = { a: "", b: "" }; for (i = 0; i &lt;= num; i += 1) { agg.a += list[i].a; } return agg; } }; } var getter = make_getter(elements); console.log(getter.get(0).a); // "a" console.log(getter.get(1).a); // "ac" console.log(getter.get(2).a); // "ace" </code></pre> <p>You can make different implementations of the aggregation function.</p> <p>With recursion:</p> <pre><code>var elements = [ { a:"a", b:"b"}, {a:"c", b:"d"}, {a:"e", b:"f"} ]; function getter(list, num) { var i, agg = list[num]; if (num &gt; 0) { agg.a = getter(list, num-1).a + agg.a; } return agg; } console.log(getter(elements, 0).a); // "a" console.log(getter(elements, 1).a); // "ac" console.log(getter(elements, 2).a); // "aace" &lt;-- note, elements are actually modified! console.log(getter(elements, 2).a); // "aaacaace" &lt;-- note, elements are actually modified! </code></pre> <hr> <p><strong>old answer</strong></p> <p>Since <code>x</code> is not an object it's value will be copied, rather than passed as a reference.</p> <p>If you change your code to:</p> <pre><code>var element = { a: '', b:'' }; myArray = [ {a:'a', b:'b'}, {a:'c', b:'d'}, element ]; for (i = 0; i &lt; myArray.length; i += 1) { element.a = myArray[i].a + myArray[i].b; } alert(el.a); // alerts 'cd'; </code></pre> <p>You will get <code>"cd"</code>.</p> <hr> <p>This is not called lazy evaluation by the way. It's just an aggregate or something.</p>
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    1. POHow to do lazy evaluation of an array being processed by a for loop
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    1. COI see that and it does help, but I have many such arrays with all variety of json objects and various properties. So it would be difficult to separately defined each of these elements. Is there a way to tell Javascript to wait on evaluating x (not do it in the initial assigned of myArray), and to evaluate each array element when it is referred to in the loop. For example, x could be a more complex statement than just a variable. I don't want to use 'eval' either. Thank you.
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    2. COPlease explain your problem better.
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    3. COEach, but not all, of the array elements are dependent on the results from processing a prior array element. The example I gave was very simple. But x could be dependant on what prior myArray iterations created or changed. I don't want to have x be evaluated until it is it's turn to be evaluated (on the 3rd iteration). I may even have more elements after this with other variables which are to be evaluated when it comes their turn. Basically, I don't want variables to be evaluated until it's their turn in the processing of the array elements. Hope that helps.
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