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blocks:tasks [2019-04-16 19:16]
admin 		blocks:tasks [2025-02-24 19:48] (current)
admin [Tasks and Expressions]
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 While the //Trigger// is the mere occurrence of the specified event (such as the time being 8:00 in the morning), the //Trigger Condition// can apply arbitrarily complex conditions on top of this event in order to decide whether to actually start the task. For instance, in the case of a time-of-day trigger, you can specify that it should only start the task if it's Saturday and a certain Block is playing on a particular Spot. While the //Trigger// is the mere occurrence of the specified event (such as the time being 8:00 in the morning), the //Trigger Condition// can apply arbitrarily complex conditions on top of this event in order to decide whether to actually start the task. For instance, in the case of a time-of-day trigger, you can specify that it should only start the task if it's Saturday and a certain Block is playing on a particular Spot.
  
-A //Trigger Condition// often uses the predefined variable named //trigger//, as in the example shown above. This variable is further described below under "Predefined Variables". You can, however, use any variable or system property in the condition.+A //Trigger Condition// often uses the predefined variable named //trigger//, as in the example shown above. This variable is further described below under "Predefined Variables". You can, however, use any system property in the condition.
  
 ===== JavaScript Expressions ===== ===== JavaScript Expressions =====
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 Expressions in Blocks use JavaScript syntax. There are numerous excellent sources of information on this subject, such as this one: Expressions in Blocks use JavaScript syntax. There are numerous excellent sources of information on this subject, such as this one:
  
-https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operator+[[https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators]]
  
 Here we'll only provide a brief overview of the syntax, enough to get you started with programming of Tasks in Blocks. Here we'll only provide a brief overview of the syntax, enough to get you started with programming of Tasks in Blocks.
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 === Relational Operators === === Relational Operators ===
  
-Another type of operators allow you to compare things, such as numbers. As hey evaluate the //relation// of two values to each other, they are often called //relational operators//. They all result in a boolean value. Examples of relational operators include:+Another type of operators allow you to compare things, such as numbers. As they evaluate the //relation// of two values to each other, they are often called //relational operators//. They all result in a boolean value. Examples of relational operators include:
  
   * < for "left is less than right".   * < for "left is less than right".
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 ===== Variables ===== ===== Variables =====
  
-The true power of expressions come from the use of variables. A variable essentially names a "mailbox" in which a value is stored. When you reference the name of that "mailbox", what you get is the value in it. In Blocks, you can use pretty much any state in the entire system as such a value source. For instance, if you have a contact closure input connected through a Modbus box, the state of that input can referenced. +The true power of expressions comes from the use of variables. A variable essentially names a "mailbox" in which a value is stored. When you reference the name of that "mailbox", what you get is the value in it. In Blocks, you can use pretty much any state in the entire system as such a value source. For instance, if you have a contact closure input connected through a Modbus box, the state of that input can referenced. 
  
 As an example, to trigger a task only if a certain input signal is present, simply refer to the value of that input in the trigger condition: As an example, to trigger a task only if a certain input signal is present, simply refer to the value of that input in the trigger condition:
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 ==== Predefined Variables ==== ==== Predefined Variables ====
  
-In addition to all system properties of you Blocks system, you also have access to the following predefined variables in tasks and their trigger condition field:+In addition to all system properties of your Blocks system, you also have access to the following predefined variables in tasks and their trigger condition field:
  
   * **trigger** contains the value of whatever triggered the task.   * **trigger** contains the value of whatever triggered the task.
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   * If the triggering mode is “Time of Day”; it's a JavaScript Date object.   * If the triggering mode is “Time of Day”; it's a JavaScript Date object.
-  * If the triggering mode is “Property Change” it's a number, boolean or string containing the property’s new value.+  * For “Property Change” it's a number, boolean, string or other object indicating the property’s new state. 
 +  * For "Server Startup", the value of //trigger// is undefined.
  
 If no trigger is assigned to the task, the value of //trigger// is undefined, and should not be used. Note that //trigger// will contain the current value of the tasks trigger even if the task was started by other means, such as manually clicking the //play// arrow next to the task's name, or by setting the task's //running// property to true. If no trigger is assigned to the task, the value of //trigger// is undefined, and should not be used. Note that //trigger// will contain the current value of the tasks trigger even if the task was started by other means, such as manually clicking the //play// arrow next to the task's name, or by setting the task's //running// property to true.
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 ==== Realm Variables ==== ==== Realm Variables ====
  
-You can add externally visible variables to a Realm. When doing o, you specify the data type used by that variable (number, boolean or string). Such a variable can be set frmo the outside, for example using a button on a panel, or by another task (using a //set realm variable// statement).+You can add externally visible variables to a Realm. When doing so, you specify the data type used by that variable (number, boolean or string). Such a variable can be set frmo the outside, for example using a button on a panel, or by another task (using a //set realm variable// statement).
  
 The value of such a realm variable can be used as a trigger, just like any other system property. You can also directly reference the value of a realm variable in any task within the same realm using the name of the variable followed by a period and the work //value//. Assuming you have a realm variable named //Brightness//, you can use its value in an expression like this: The value of such a realm variable can be used as a trigger, just like any other system property. You can also directly reference the value of a realm variable in any task within the same realm using the name of the variable followed by a period and the work //value//. Assuming you have a realm variable named //Brightness//, you can use its value in an expression like this:
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 ==== Property References ==== ==== Property References ====
  
-As seen in some of the example above, you can set the value of any property in your Blocks system using a //do// statement. You can pick the target of the //do// statement using the dropdown menus to the right. Alternatively, if you know the full path to the desired property, you can type this into the //do// statement's target field.+As seen in some of the examples above, you can set the value of any property in your Blocks system using a //do// statement. You can pick the target of the //do// statement using the dropdown menus to the right. Alternatively, if you know the full path to the desired property, you can type this into the //do// statement's target field.
  
-Some properties are //read only//. An example of such a read only property is the //connected// state of a Display Spot. There's nothing you can do from within Blocks to force a Spot to connect. Thus, this property can only be read, not set. Read only properties are shown in //italics// on dropdown menus. They can not be used as the target property of a //do//statement. They can, however, be used in expressions and task triggers.+Some properties are //read only//. An example of such a read only property is the //connected// state of a Display Spot. There's nothing you can do from within Blocks to force a Spot to connect. Thus, this property can only be read, not set. Read only properties are shown in //italics// on dropdown menus. They can not be used as the target property of a //do// statement. They can, however, be used in expressions and task triggers.
  
 The value of a system property can also be directly used in expressions. Since such an expression typically consists of more than just a single property reference, you need to enter the full path to the property manually here.  The value of a system property can also be directly used in expressions. Since such an expression typically consists of more than just a single property reference, you need to enter the full path to the property manually here. 
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 </code> </code>
  
-The expression inside the brackets performa string concatenation, so that if the /7channel// realm variable contains 2, the resulting string will be "c2", thus controlling the channel with that name.+The expression inside the brackets performa string concatenation, so that if the //channel// realm variable contains 2, the resulting string will be "c2", thus controlling the channel with that name.