Xponent uses Expressions extensively within Business Logic and for Conditional branches in graphs. Each expression can be defined in one of two ways: Basic or Advanced. Both of these techniques generate a JavaScript expression, which is evaluated for truthfulness.
Basic Expressions
Basic expressions provide a dropdown list of common expressions which are available to be used:
Selecting Advanced from the dropdown shows a JavaScript expression window that allows any valid JavaScript Boolean expression to be entered.
By default, the equivalent JavaScript will be shown when switching from the Basic to the Advanced view.
| Basic Expression | Arguments | Equivalent JavaScript | Note |
|---|---|---|---|
| Is True | None | VAL === true | |
| Is False | None | VAL === false | |
| Less Than or Equal To | Constant Value - numeric or string | VAL <= 12.3 | |
| Greater Than | Constant Value - numeric or string | VAL > 12.3 | |
| Greater Than or Equal To | Constant Value - numeric or string | VAL >= 12.3 | |
| Equals | Constant Value - numeric, string, or boolean | VAL == {...} | |
| Not Equal To | Constant Value - numeric, string, or boolean | VAL != {...} | |
| Contains | Constant String | VAL.indexOf('abc') > -1 | This method is case-sensitive. Make sure you manipulate as necessary to make it case insensitive. |
| Starts With | Constant String | VAL.indexOf("abc") === 0 | This method is case-sensitive. Make sure you manipulate as necessary to make it case insensitive. |
| Ends With | Constant String | VAL.lastIndexOf("abc") === VAL.length - "abc".length | This method is case-sensitive. Make sure you manipulate as necessary to make it case insensitive. |
Advanced Expressions
Advanced expressions are any valid boolean JavaScript (ECMAScript 5) expressions. The JavaScript variable 'VAL' is always available and is set to the Value of the previous node when used as an expression on a conditional branch.
If the Basic Expressions do not have the type of operator that you require, then the advanced mode should allow you to program your own condition. Examples include:
| Description | Conditional | JavaScript |
|---|---|---|
| Membership of a list. Test to see if the returned Value is in a list of values. |  | |
| Check if a javascript object is empty or not |  | Object.keys(obj).length === 0 && obj.constructor === Object |
Miscellany
It is worth taking note that JavaScript has some interesting outcomes when compared against null:
- null >= 0 → true
- null <= 0 → true
- null == 0 → false
- +null == 0 → true