Handlebars` 模板占位符的默认值

Question

Can I specify a default value for a Handlebars` template placeholder?

<script type="x-handlebars-template" id="menu-edit-form-tpl">
    <form method="{{method}}" action="{{action}}" class="menu-edit-form">
...                     
    </form>
</script>

Can I specify default values for {{method}} and {{action}} and skip them in the object that is passed to the compiled template?

Answer 1

Handlebars has no "default values".
You should use {{#if}} statement to check property is set.

<script type="x-handlebars-template" id="menu-edit-form-tpl">
    <form method="{{#if method}}{{method}}{{else}}POST{{/if}}" action="{{#if action}}{{action}}{{else}}/{{/if}}" class="menu-edit-form">
...
    </form>
</script>

Or if you want a bit cleaner syntax, use the simple helper:

Handlebars.registerHelper('safeVal', function (value, safeValue) {
    var out = value || safeValue;
    return new Handlebars.SafeString(out);
});

which allows you to write like this:

<script type="x-handlebars-template" id="menu-edit-form-tpl">
    <form method="{{safeVal method 'POST'}}" action="{{safeVal action '/'}}" class="menu-edit-form">
...
    </form>
</script>

Answer 2

Here is my simple solution

first we create a very basic helper called 'choose'

    Handlebars.registerHelper('choose', function (a, b) {return a ? a : b;});

then we use it in the template :)

<p>
{{choose valueFromData 'default-value-in-template'}}
<p>

or of course we can do

    <p>
    {{choose valueFromData defaultValueFromData}}
    <p>

So in your case:

<form method="{{choose method 'get'}}" action="{{choose action 'action.php'}}" class="menu-edit-form">
...                     
    </form>

Hope it helps someone else since this is from 2014 :)

Answer 3

This question and its accepted answer are quite old and a lot of new features and functionality have been added to handlebars since they were written.

I managed to get the functionality of default values by using partial blocks which were released in v4.0.0 - so your template would end up looking like this:

<script type="x-handlebars-template" id="menu-edit-form-tpl">
    <form method="{{#> method}}get{{/method}}" action="{{#> action}}index.php{{/action}}" class="menu-edit-form">
...                     
    </form>
</script>

Then it's just a case of passing in your method and action as partials by doing something like this:

var source = $('#menu-edit-form-tpl').html(),
    template = Handlebars.compile(source),
    html = template({}, {
        partials: {
            action: 'contact-form.php'
        }
    });

In the resulting html the method will default to get and the action will be contact-form.php . Here's a working demo:

 var source = $('#menu-edit-form-tpl').html(), template = Handlebars.compile(source), html = template({}, { partials: { action: 'contact-form.php' } }); // Code below here only to show output. document.write('<code>' + $("<div/>").text(html).html() + '</code>');

 <script src="https://cdnjs.cloudflare.com/ajax/libs/handlebars.js/4.0.5/handlebars.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <script type="x-handlebars-template" id="menu-edit-form-tpl"> <form method="{{#> method}}get{{/method}}" action="{{#> action}}index.php{{/action}}" class="menu-edit-form"> ... </form> </script>

Answer 4

You can register a helperMissing helper which will get called whenever a value is defined in your template, but not in your context (useful if you don't want missing values to fail silently):

Handlebars.registerHelper("helperMissing", function(context, options) {
    console.error("Template defines {{" + context.name + "}}, but not provided in context");
    return "{{" + context.name + "}}";
});