Handlebars.js if block helper ==

问题

How would you change the following code to make it work? The problem is the this == \'some message\' expression:

<ul>
  {{#each errors}}
    {{#if (this == \'some message\') }}
    <li>Status</li>
    {{else}}
    <li>{{this}}</li>
    {{/if}}
  {{/each}}
</ul>

回答1:

The easiest thing would be to add a custom if_eq helper:

Handlebars.registerHelper('if_eq', function(a, b, opts) {
    if(a == b) // Or === depending on your needs
        return opts.fn(this);
    else
        return opts.inverse(this);
});

and then adjust your template:

{{#if_eq this "some message"}}
    ...
{{else}}
    ...
{{/if_eq}}

Demo: http://jsfiddle.net/ambiguous/d4adQ/

If your errors entries weren't simple strings then you could add "is this some message" flags to them and use a standard {{#if}} (note that adding a property directly to a string won't work that well):

for(var i = 0; i < errors.length; ++i)
    errors[i] = { msg: errors[i], is_status: errors[i] === 'some message' };

and:

{{#if is_status}}
    <li>Status</li>
{{else}}
    <li>{{msg}}</li>
{{/if}}

Demo: http://jsfiddle.net/ambiguous/9sFm7/

回答2:

Old question, but if you use Elving's Swag Handlebars helpers library, you can use the helpers is and isnt.

回答3:

This can also be achieved by using Handlebars Subexpressions.

Template -

    <script id="tmplStatus" type="text/x-handlebars">
        <ul>
            {{#each errors}}
                {{#if (is_status this 'some message')}}
                    <li>Status</li>
                {{else}}
                    <li>{{this}}</li>
                {{/if}}
            {{/each}}
        </ul>
    </script>

Javascript -

var errors = [
        'Where is pancakes house?',
        'some message',
        'One cent stamp'
    ];

    Handlebars.registerHelper('is_status', function(msg, matchMsg, options) 
    {
        if(msg === matchMsg)
            return true;
        else
            return false;
    });

    var tmplStatus = Handlebars.compile($('#tmplStatus').html()),
        domStatus = tmplStatus({ errors: errors });
    $('body').append(domStatus);

Working Demo : http://jsfiddle.net/techgeeek/b99qwtpw/

来源：https://stackoverflow.com/questions/15088215/handlebars-js-if-block-helper

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