# vs $ in the computed expressions in the xpages

In the xml code of the xpages the computed expressions begin with the character “#” or with the character “$”, ie they are one of the following types:

• value=”#{[language]:[expression]}”
• value=”${[language]:[expression]}”

where [language] is the name of the language, for example javascript and [expression] is the expression to compute.

The question is “what is the difference between the two cases?”.
To answer this question, consider the following example:

<?xml version="1.0" encoding="UTF-8"?>
<xp:view xmlns:xp="http://www.ibm.com/xsp/core" xmlns:xp_1="http://www.ibm.com/xsp/coreex">

	<xp:label id="label1" style="font-size:18pt;font-weight:bold"
		value="# vs

quot;> </xp:label> <xp:br></xp:br> <xp:br></xp:br> <xp:table border="1" cellpadding="4"> <xp:tr> <xp:td> <xp:label value="using #" id="label2"></xp:label> </xp:td> <xp:td> <xp:text escape="true" id="computedField1" value="#{javascript:new Date().toLocaleString();}"> </xp:text> </xp:td> </xp:tr> <xp:tr> <xp:td> <xp:label id="label3" value="using

quot;></xp:label> </xp:td> <xp:td> <xp:text escape="true" id="computedField2" value="${javascript:new Date().toLocaleString();}"> </xp:text> </xp:td> </xp:tr> </xp:table> <xp:br></xp:br> <xp:button value="Refresh" id="button1"> <xp:eventHandler event="onclick" submit="true" refreshMode="complete"> <xp:this.action> <xp:saveDocument></xp:saveDocument> </xp:this.action> </xp:eventHandler> </xp:button> <xp:br></xp:br> </xp:view>

this xpage contains two Computed Field controls that display the current date and a button to refresh the page.
If you open the xpage with a browser it looks like the following figure:

with equal times.
Then if you perform a refresh using the button, the page becomes:

with different times because only the computed field with the character “#” is updated.
So now you can answer the question above:

• • value=”#{[language]:[expression]}” is computed at each update of the page
  • value=”${[language]:[expression]}” is computed only once at the first loading of the page

In the designer client you get the two cases selecting the property “Value” of the Computed Field control “Compute dynamically” o “Compute on page load” as in figure: