Is there a ternary operator in handlebars.js?

问题:

In Handlebars, is there a ternary operator? I don't mean if else; I mean like a == true ? "a" : "b".

回答1:

You can build your own helper in handlbars if you really want to. Something like ternary(a==true, "a", "b"). For more information on that see the documentation. The idea from m90 is not the idea behind handlebars. The idea is to not have explicit code in your templates, only calls to helpers and objects.

回答2:

The if helper can be used as a ternary operator by passing three arguments to it.

In the following example, a button has a default value of "Save Changes", but when model.isSaving is true, then the value temporarily changes to Saving....

<button>{{if model.isSaving "Saving..." "Save Changes"}}</button>

...alternatively, used within another helper:

{{input type="submit" value=(if model.isSaving "Saving..." "Save Changes")}}

回答3:

I have a helper for this (pay attention that other helpers can also be used inside) https://gist.github.com/terion-name/d87ed8907f1bb2e25f32

// app/helpers/iftrue.js
import Ember from 'ember';

export function iftrue(params) {
  if (params[0]) {
    return params.length === 2 ? params[0] : params[1];
  }
  if (params.length === 2) {
    return params[1];
  } else if (params.length === 3) {
    return params[2];
  }
  return null;
}

export default Ember.Helper.helper(iftrue);

With two parameters: if first parameter evaluates to true it will be printed, otherwise second

{{iftrue project.price 'N/A'}} // $9.99
{{iftrue project.priceNotAvailable 'N/A'}} // N/A

With three parameters: if first parameter evaluates to true second will be printed, otherwise third

// If deadline is set formatted date will be printed, otherwise 'N/A'
{{iftrue project.deadline (moment-format project.deadline 'DD.MM.YYYY') 'N/A'}} 

回答4:

This below code can be used for ternary or any kind of expression eval.

Warning: please use this code in scenario where eval can be used safely.

{{#if (myfunc "(a[0] + 1) % 2 === 0" arg1)}}

{{/if}}

{{#if (myfunc "(a[0] + a[1]) % 2 === 0" arg1 arg2)}}

{{/if}}

handlebar helper function

myfunc: (exp, ...a) => {
    return eval(exp);
  }