What is true or false in Mustache and Rulber?

Question

In JavaScript:

falsy: false, null, undefined, 0, -0, NaN, "" truthy: everything else, including [] and {} (empty array and empty object) 

But in Handlebars it seems like this (from Handlebars Docs ) for {{#if foo}} :

 falsy: false, undefined, null, "", [] truthy: everything else, including 0, -0, {} 

undefined and NaN cannot be specified as a value in the JSON file, so I cannot test it using the Java Mustache renderer, although if I don't define a property at all, it's probably just undefined , and this is taken as a lie.

Above for {{#if foo}} , and to make things more complicated, but what about {{#foo}} in Handlebars and Mustache? Are fake rules and rules the same as {{#if foo}} ? If possible, provide pointers to documents to support your request. We hope that the implementation of Mustache or Handlebars in PHP or Java or in other languages ​​follows exactly the same rules.

I also found that for Mustache it seems that {{#foo}} is called a section, and its rule is:

 falsy: whatever falsy in JavaScript, plus [] truthy: everything else 

But it seems that the implementation of can.js Mustache / Handlebars treats 0 as fake. ( http://jsfiddle.net/kAt7E/45/ vs http://jsfiddle.net/kAt7E/46/ or http://jsfiddle.net/kAt7E/47/ vs http://jsfiddle.net/kAt7E/ 48 / ). So it is somewhat worrying that there are so many different rules.

Answer 1

According to the Mustache specification , veracity depends on the host language. There have been several attempts to standardize this in different languages, but the consensus was that the host language had the last word.

The value, in JavaScript, is everything for which !!val === true is true, and everything where !!val === false false. If different Mustache implementations in the same language are incompatible with this specification, this is an implementation error.