如何计算html / template中的内容

Question

How can you calculate something inside a html template of go?

For example:

{{ $length := len . }}
<p>The last index of this map is: {{ $length -1 }} </p>

Were the . is a map.
The code {{ $length -1 }} is not working, is there a way to achieve this?

Answer 1

You can't. Templates are not a scripting language. By design philosophy, complex logic should be outside of templates.

Either pass the calculated result as a parameter (preferred / easiest), or register custom functions which you can call during template execution, pass values to them and which may perform calculations and return any values (e.g. return param - 1).

For examples of registering and using custom functions, see:

Golang templates (and passing funcs to template)

How do I access object field by variable in template?

Iterate Go map get index.