Handlebars return an array element with certain index if the length is unknown

Question

Using Handlebars and Node, I have an array with changing length and I need always to get the one before last element of it each time it changes.

So if you want to get the last element, you can do:

{{#each array}}
  {{#if @last}}
    {{this}}
  {{/if}}
{{/each}}

and it will return you the last element. I have Math helper, that can perform basic mathematical operations. For example I can get with it the needed index number

{{math array.length '-' 1}}

but I cant use it with another block helper, for example:

{{#each array}}
  {{#if math @last '-' 1}}
    {{this}}
  {{/if}}
{{/each}}

How could this be done? Thank you.

Answer 1

You can register your own helper for that:

Handlebars.registerHelper('isSecondLastArrayItem', function(array, index, options) {

  if((array.length - 2) === index)
    return options.fn(this);

  return;

});

And use it like this:

{{#each array}}
  {{#isSecondLastArrayItem @root.array @index}}
    {{title}}
  {{/isSecondLastArrayItem}}
{{/each}}

Example data:

{ 
  array: [{ title: 'aa' }, { title: 'vv' }]
}

Try it out in the sandbox.

EDIT: case for any index

Handlebars.registerHelper('isNthLastArrayItem', function(array, index, offset, options) {

  if(((array.length >= offset) && (array.length - offset) === index)
    return options.fn(this);

  return;

});

usage (for 2nd item from the end):

{{#each array}}
  {{#isNthLastArrayItem @root.array @index 2}}
    {{title}}
  {{/isNthLastArrayItem}}
{{/each}}