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Revision as of 18:11, 14 March 2017 by Hraban (talk | contribs) (JS bug was fixed.)
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< Visuals | Interaction >

You can find more about interactive form elements in Widgets uncovered. It’s written for MkII, but still mostly valid.

Most of the following examples are from mwidget manual. We will cook up our own later.


If you need to check or otherwise process the input of your forms, you need JavaScript to handle interaction. For simple forms without input validation, you can skip this section.

\startJSpreamble {name}
MyCounter = 0 ;

\startJScode {increment}
MyCounter = MyCounter + 1 ; // or: ++MyCounter ;

\goto {advance by one} [JS(increment)]

In some versions of MkIV there was a bug that the JS code was only copied to the PDF if there was a \goto referencing one of the defined functions. Should be gone.

You can pass values to a JS function:

\startJScode {increment}
MyCounter = MyCounter + JS_V_1 ;

\goto {advance by five} [JS(increment{V{5}})]
  • V{} is verbose, defaults to string
  • S{} = as string
  • R{} = as reference
  • JS_V_n, JS_S_n, JS_R_n are the names of the variables
  • JS_N keeps the number of arguments


JavaScript in Acrobat is different than in a web context. Documentation is even more sparse than on ConTeXt ;) Debugging is only possible in Acrobat Pro, and also there very inconvenient. Additionally, Acrobat’s possibilities change with every version.


Setting a default value

Here we set a date field to the current date on opening the document. Additionally we have a button that can hide/show a form field.

\setupinteraction	[state=start]

\startJSpreamble {EXAMPLE} used now
var d = new Date();
var df = this.getField("CurDate");
df.value = util.printd("dd.mm.yyyy", d);

function toggleField(){
	var f = this.getField("CurDate");
	f.display = ! f.display;

\setupfield[shortString][reset,horizontal][height=5mm, width=50mm, frame=off, bottomframe=on]
\definefield[CurDate][line][shortString][][JavaScript should replace this text with the current date]

Current date: \field[CurDate]


Setting the current date

Similar, but more usable than the example above:


\startJSpreamble {EXAMPLE} used now
function Dummy(){
	return 0;

function setCurrentDate(fieldname) {
	var f = this.getField(fieldname);
	f.value = util.printd("yyyy-mm-dd", new Date());


\definefield[myDateField][line][dateString][][JavaScript should replace this text with the current date]

Current date: \field[myDateField]


Someone thinks this entry needs some more explanation. (See: Needs Explanation?, To-Do List.)

Relevant commands:

Field types:

  • line: one line of text
  • text: more lines of text
  • radio: radiobutton (only one of a group can be active)
  • check: checkbox
  • signature: electronic signature (since ConTeXt beta of 2016-03-11)

Beware, for fillinfields in MkIV you need \usemodule[fields]! They’re meant for clozes (texts with gaps, like in questionnaires).

In MkIV (as of 2015-04-01) default values are always used verbatim, i.e. JS() doesn’t work. (Check: other bug is gone, maybe this also?)

Other fields you must first define and then use. That might look complicated, but you can use the same field several times, and the contents will automatically repeat themselves if you need the same content at several places, even on different pages.

Text Entries

\fillinfield[name]{text that defines field length}


\definefield [Email] [line] [ShortLine] [] [sample@contextgarden.net]
\field [Email] [your email]


Example from the manual:

\setupfield [LogoSetup]

\definefield[Logos] [radio] [LogoSetup][ConTeXt,PPCHTEX,TeXUtil] [PPCHTEX]

\definesubfield [ConTeXt] [] [ConTeXtLogo]
\definesubfield [PPCHTEX] [] [PPCHTEXLogo]
\definesubfield [TeXUtil] [] [TeXUtilLogo]

\definesymbol [ConTeXtLogo] [{\externalfigure[mpcont.502]}]
\definesymbol [PPCHTEXLogo] [{\externalfigure[mpcont.503]}]
\definesymbol [TeXUtilLogo] [{\externalfigure[mpcont.504]}]

\hbox to \hsize{\hss\field[ConTeXt]\hss\field[PPCHTEX]\hss\field[TeXUtil]\hss}

As usual, first you need to define a class of fields (\setupfield). Then you define the (invisible) group of radio buttons (\definefield with "radio"). At last you define the single radio buttons with \definesubfield.

Arguments of \definefield:

  1. field name
  2. field type "radio"
  3. setup class, as defined by \setupfield
  4. list of field names that should be part of the group
  5. name of default (activated) button

Arguments of \definesubfield:

  1. field name
  2. setup class (default is inherited, but you can use a different one)
  3. content symbol, defined by \definesymbol


\setupfield[setup 3]
        [width=2cm, height=2cm,
        rulethickness=3pt, corner=round, framecolor=red]

\definesymbol [yes] [{\externalfigure[mpcont.502]}]
\definesymbol [no] []
\definefield [checkme][check] [setup 3] [yes,no] [no]

Tricks and Traps


  • JS code is only copied to the PDF if there is a \goto referencing one of the defined functions! – This is actually a feature, you can get your JS without \goto, using the magic incantation used now, as in the default value example.
  • JS code for default values doesn’t work (reported 2015-04-01, still true 2015-10-07).


This helps debugging:

\showfields  % typeset a table of field relations
\logfields     % logs field descriptions to a file fields.log