If condition is truthy, the function returns trueValue. If the condition is not truthy, this returns falseValue if supplied (or undefined otherwise).
If trueValue or falseValue is a function, it will be evaluated and its result returned instead.
Example
The origami-blog-start sample project has a singlePostPage.ori template for displaying a single post object as HTML.
In this project, a post object may contain a nextKey or previousKey value indicating the next or previous page in the sequence of blog posts. To render this value as a link, the post template includes the fragment:
if(post/previousKey, =`
<a class="previous" href="${ post/previousKey }">
Previous: ${ tree(post/previousKey)/title }
</a>
`)
This expression uses an if function to see if the post defines a previousKey value. If it does, the if function will return the second (trueValue) argument. In this case, that argument is a function defined in shorthand syntax. The if will invoke that function, which will create an HTML fragment for a link that goes to the indicated page. That HTML fragment will be returned as the result of the if.
If the post does not define a previousKey, the if will return undefined, and nothing will be displayed.
Caution
Origami’s if builtin works something like conditional operators or if statements in programming languages like JavaScript. However, those languages typically only evaluate the true or false part of the if once the value of the condition is known. If the condition is true, only then is the true branch of the if taken; the false branch will never be executed.
In contrast, the if builtin is a normal function – Origami will evaluate all of its arguments before calling the if.
For that reason, unless the true or false arguments to if are trivial numbers or strings, you will generally want to turn those arguments into a function by prefixing with = as shown above. This will defer evaluation of the argument to the point when if knows whether it’s going to need that result or not.
In particular, you will need to pass functions to if when the if is being used to check for the existence of an object that will be further traversed in the trueValue or falseValue arguments.
Example: you have a template that may need to render a user object and, if there is a user, to show their name. The following if will not work:
// Won't work
if(user, user/name)
This expression won’t work because, if user doesn’t exist, then the expression user/name will fail. That will happen before the if statement has a chance to check whether user exists or not.
To avoid this problem, pass a function to if:
// Use a function to defer looking up the user's name
if(user, =user/name)
The expression =user/name will be evaluated before the if is called but will just define a function. That function won’t be called until if checks to see whether user exists. Only if the user exists will the =user/name function be called.