Question

193

boolean logic within a handlebars template

rated 0 times [ 198] [ 5] / answers: 1 / hits: 30401 / 12 Years ago, tue, february 12, 2013, 12:00:00

Is it possible to perform boolean logic within a handlebars conditional?

Right now I spoof this behavior with a controller function, so I end up with the controller

App.ApplicationController = Ember.Controller.extend({

    bool1: true,

    bool2: true,

    both: function(){ return this.bool1 && this.bool2; }.property('content.both'),

});

Which allows me to use a handlebars template of

<script type=text/x-handlebars>

  {{#if both}}

     <p> both were true </p>

  {{/if}}

</script>

and that works fine, but raises some problems. First off, it obscures what's happening (particularly if good function names aren't used). Secondly, it seems to infringes a bit on the MVC separation.

Is it possible to do something along the lines of

<script type=text/x-handlebars>

  {{#if bool1 && bool2}}  <!-- this will not actually work -->

     <p> both were true </p>

  {{/if}}

</script>

and have it work?

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magdalena

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2 Years ago

answered 12 Years ago domeniccolti · Accepted Answer

You can't do it directly but it isn't that hard to do with a little bit of arguments parsing and a variadic helper. Something like this:

Handlebars.registerHelper('if_all', function() {

    var args = [].slice.apply(arguments);

    var opts = args.pop();



    var fn = opts.fn;

    for(var i = 0; i < args.length; ++i) {

        if(args[i])

            continue;

        fn = opts.inverse;

        break;

    }

    return fn(this);

});

And then in a template you can say:

{{#if_all a b c}}

    yes

{{else}}

    no

{{/if_all}}

You can use as many arguments to {{#if_all}} as you need. You might want to adjust the truthiness test to match Handlebars since {{#if}} treats

`false`, `undefined`, `null`, `` or `[]` (a falsy value)

as falsey and everything else as truthy whereas [] is truthy in JavaScript.

Demo: http://jsfiddle.net/ambiguous/vrb2h/