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--- JXA_JavaScript_for_Applications [2016/01/05 15:12]
ComplexPoint [Attaching reusable names to evaluations and their results:]
+++ JXA_JavaScript_for_Applications [2016/01/06 21:17]
peternlewis deleted in favor of JavaScript for Automation
@@ Line 61: / Line 61: @@
 | <code>count of documents of application "TextEdit"    </code> | <code>Application("TextEdit").documents.length    </code> |
-====Attaching reusable names to evaluations and their results:====
+====Attaching reusable names to computations and their results:====
-If we often need to calculate the Golden Ratio, we can attach a name to its computation, and reuse it by that name. Nameable computations are called 'handlers' in AppleScript, and 'functions' in JavaScript.
+If we often need to calculate the [[https://en.wikipedia.org/wiki/Golden_ratio|Golden Ratio]], we can attach a name to its computation, and reuse it by that name. Nameable computations are called 'handlers' in AppleScript, and 'functions' in JavaScript.
 ===Named computations – handlers and functions===
@@ Line 111: / Line 111: @@
 ^ AppleScript    ^ JXA  ^
 | <code>on goldenRatio(n)
     return (((sqrt 5) + 1) / 2) * n
 end goldenRatio
@@ Line 140: / Line 140: @@
 JavaScript is relaxed about whether we supply an argument or not. If we don't, the name ''n'' will have the special value ''undefined'', which takes on the value ''false'' in a logical expression. Above we are using the [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators|JavaScript logical operator OR ( || )]] to attach the name n to the value 1 if no argument has been supplied.
-===Named results of computations – variables which hold values===
+===Named results of computations – 'variables' which hold values===
+In addition to reusable names for particular computations and their arguments, we can also give names to the results of computations. Once a result is stored in a named variable, we can reuse it without having to recalculate it.
+^ AppleScript    ^ JXA  ^
+| <code>on run {}
+    set phi to (((sqrt 5) + 1) / 2)
+    set phi18 to phi * 18
+    set phi7 to phi * 7
+    return phi18 + phi7
+end run
+--> 40.450849718747</code> | <code>function run() {
+    var phi = (Math.sqrt(5) + 1) / 2,
+        phi18 = phi * 18,
+        phi7 = phi * 7;
+    return phi18 + phi7;
+}
+// --> 40.45084971874737</code>|
+==Things to notice – 1. We gave the name 'run' to a computation, and it 'ran' without being called …==
+In osascript (AppleScript or JXA), **run** is a special name. A handler or function with that name is called automatically – you don't have to append parentheses to call it, like we did with the **goldenRatio** computation.
+In fact, when we don't assign any names to computations (don't create any AS handlers or JS functions), osascript automatically wraps our our script in a computation which it names **run**, and immediately calls it.
+==Things to notice - 2. We are attach names here to some results of computations==
+The following names are all given to the result of a computation, rather than to a computation or argument:
+- phi
+- phi18
+- phi7
+==Differences to notice: AS and JS use different patterns for naming results==
+Where AS uses the pattern:    **set** *name* **to** *resultingValue* (and reserves **=** for testing equality),
+JS uses one or more [[https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Statements/var|variable declaration statements]] (and [[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness|tests equality]] with **===**)
+In JS we can either:
+- group several variable declarations together (separated by commas, finishing with a semicolon – example above),
+- use a separate variable declaration statement for each variable, or
+- make our lives more complex by using the names without a var declaration
+^ Good and simple JXA – temporary local names ^  Messy and complex JXA – persistent global names ^
+|<code>    var phi = (Math.sqrt(5) + 1) / 2,
+        phi18 = phi * 18,
+        phi7 = phi * 7;
+// or
+    var phi = (Math.sqrt(5) + 1) / 2;
+    var phi18 = phi * 18;
+    var phi7 = phi * 7;</code>|<code>    phi = (Math.sqrt(5) + 1) / 2;
+    phi18 = phi * 18;
+    phi7 = phi * 7;</code>|
+JavaScript gives us a lot of freedom, [[http://shop.oreilly.com/product/9780596517748.do|sometimes more than is helpful]]. Misspelled variable names, and accidental uses of the same globally visible name in different parts of a script are rich sources of puzzling bugs and wasted time. To use a less liberal but more helpful set of JavaScript rules, we can add the line **'use strict';**
+at the start of a function. When we do this, JavaScript checks that all of our variables are declared (and therefore 'local' – visible only to their containing functions, and also temporary – vanishing when the evaluation of a function is completed). If an undeclared variable name is detected when the **'use strict';** statement has been added, we are given a helpful warning:
+{{::use-strictpng.png|}}
+====Structuring collections – indexing by number, and by name===
+to follow ...
+====Structuring computations – branching, repetition, and nested composition====
+to follow ...
+====JSON for persistence – saving things between macro runs, and reading them straight back in====
+to follow ...
+=====The Automation interface=====
+===Using the Standard Additions library====
+to follow ...
+===Interacting with scriptable applications===
+to follow ...
+=====Using the Safari JSContexts Debugger (El Capitan onwards)=====
+to follow ...
+=====The ObjC interface=====
+to follow ...
+===Basic file functions===
+to follow ...
+===Clipboard functions===
+to follow ...
-(to be added)
+===Reading the documentation for simple ObjC functions===
+to follow ...

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