Updater examples with Scriptalicious & Seaside

The first of a series of coding vignettes in Seaside.

 Context: a web app with a form containing multiple input fields.  Instead of waiting to submit the form, I want the page to update another element every time an input is changed.  In this example, a total field.  Solution was used for a simple MoneyCounter application:

MoneyCounter>>renderContentOn: html html form id: 'f'; with: [

html table: [
    html tableRow:
     [html tableData: [html text: 'pennies'];
         [html textInput
           id: 'pennies';
 	   "on: #pennies of: self;"
           callback: [:value | self pennies: value];
 	   onChange: (html updater
                       id: 'total';
		       triggerFormElement: 'pennies';
 		       callback: [ :r  |  self renderTotalOn: r])
       ] ]


    html tableRow:
      [html tableData: [html text: 'TOTAL'; space];
            tableData: [html span id: 'total' ; with: self total]]]]

MoneyCounter>>renderTotalOn: html

 html render: self total
MoneyCounter>>pennies: value
   pennies := value

	^((pennies asInteger * 0.01) +  etc.   )

The real action demonstrated here is in onChange: . onChange will accept a Javascript function or an SUUpdater to automagically do the Javascript functioning. html updater returns just such an SUUpdater, and the two important things this updater does is a define a callback block of code – this block will be called everytime onChange is triggered – in this case, to renderTotalOn. Important, though, for this block to work correctly, is to also call triggerFormElement. This will trigger the callback block on the element itself, callback: [:value | self pennies: value], then also do the  updater callback. Without the triggerFormElement, calling renderTotalOn will update the total with the “old” value of pennies, instead of what the user had currently entered.

In simple English, whenever the input field is changed, update the value that is bound to the field, then update the Total field.

For this to work appropriately, it’s also important to set element ids correctly.   The updater also seems to require an id – and seemingly that id must be the same as the element that it is updating, but I’m not exactly clear on this yet.

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I'm the founder and president of Agoric Source, LLC, co-organizer of the Houston Python Meetup, and active board member of several local non-profit organizations, including Ten Thousand Villages Houston, the Houston Area Model United Nations, and the Weekley Family YMCA. I'm first and foremost still a software hacker, but with my economics background and business experience, I serve well as a project or program manager, technical visionary, etc. I'm opinionated, but hopefully reasonable so. My blog is just a chance for me to keep up with my writing skills, and expound upon various technology and policy subjects. I especially try to keep up with the Houston software community.