Tips:Using JavaScript in Memento

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These are tips & techniques for using JavaScript for expressions in JavaScript fields and for scripts in triggers.

FIELD tips

Tips for various field types.

Field Type Return Values
Field type JavaScript object Examples
Text , Hyperlink, Password, Phone, Email, Barcode, Radio buttons, Single-choice list, Calculation (string result) String "abc"
Integer, Real number, Integer values, Rating, Currency, Calculation (number result) Number 42, 42.1
Date , DateTime, Time Date
Checkbox (Boolean) Boolean true, false
Checkboxes, Multiple-choice list Array of strings ["Shirts", "Pants", "Socks"]
Image Array of strings ["file:///storage/emulated/0/DCIM/image01.png", "file:///storage/emulated/0/DCIM/image02.png"]
Link to entry Array of entries
Each array element has a method field() for access to values of fields of entries of the linked library. Example:
field("localField")[i].field("remoteField")
[e1, e2, e3, ...]

Simple fields

Field that function as JavaScript type String, Number, Boolean, and Date operate in a direct manner. For example:

JavaScript field
field("linkedLib.integerField")*100
Trigger script
entry().set("percent", field("linkedLib.integerField")*100);

Multiple-choice fields

TBD

Link to Entry fields

The Link to Entry field has its own structure, unique among the field types.

Using field() to access the value of local and remote field values

Argument
  1. The name of the field whose value you want
Returns
An array of Entry objects.
To access fields in the linked library, use:
JavaScript field
var links = field("Link field name");
if (links.length > 0) {
    var name = field(links[0].field("Name");
    // Put your code to handle name here
    }
Trigger
var e = entry(), links = e.field("Link field name");
if (links.length > 0) {
    var name = e.field(links[0].field("Name"));
    // Put your code to handle name here
    }


Using set() in a trigger to set the value of a local field

Arguments
  1. Name of the field whose value is to be set
  2. Comma-separated list of Entry Names
To set a link field to point to an entry of another library and set another link field to point to two entries, use:
Trigger
var e = entry();
e.set("First link", "InterOpera Group");
e.set("Second link", "Mozilla,Google");


To copy a link's value to another link

  • The remote library must be set to use unique Entry Names.
  • Both links must point to the same library
Trigger
var e = entry(),
    library = "Software firms",
    from = "First link",
    to = "Second link",
    lib = libByName(library);
if (lib != null) {
    // Copy the link
    var entryNames = [],
        entries = e.field(from);
    for (var i in entries)
        entryNames.push(entries[i].title);
    e.set(to, entryNames.join());
    }

How Trigger & JavaScript field scripts differ

You'll notice in this page that the code for JavaScript fields and that for triggers are very similar, but also that they different. Here's how they are different:

Context

  • Context is set for you in a JavaScript field, and that context is the current entry. So, if you call field(), that implicitly invokes the field() function on the current entry.
  • Context is not set in a trigger, so only global functions are initially available, and using those, you can set up context for functions you want to call on the objects you're interested in.
JavaScript field
field("Fraction") * 100
Trigger
var e = entry(), lib = lib();
message("Library " + lib.title + ", entry " + e.title);

Semicolons

To make things as simple and straightforward as possible, not only is context set up for you in JavaScript fields, but the need for using JavaScript semicolons is removed.

If you know where to put semicolons, their use is recommended, to guarantee clarity and correctness. However, if you aren't sure about such things, you can omit them, and most of the time there will be no consequences. Most JavaScript fields are just one or two lines long, so the need for statement terminators is minimal.

Trigger scripts are straight JavaScript, so the code must obey JavaScript rules, including statement terminators.

Links

JavaScript field, Triggers, Trigger Examples

W3Schools
JavaScript Tutorial A pleasant, fairly complete, and useful tutorial on JavaScript
Best on a computer or tablet in landscape. On a phone or tablet in portrait, scroll to the bottom for navigation.
Mozilla Developer Network
JavaScript Guide Shows you how to use JavaScript, gives an overview of the language, and presents its capabilities & features
JavaScript Reference The entire JavaScript language described in detail
Introduction to JavaScript Introduces JavaScript and discusses some of its fundamental concepts
JavaScript Tutorial A re-introduction. JavaScript is often derided as being a toy, but beneath its simplicity, powerful language features await.
JavaScript 1.7 The JavaScript release upon which Memento is currently based
About JavaScript Jumping off point in learning about JavaScript