handlebars.js {{#if}} 条件中的逻辑运算符

Question

Is there a way in handlebars JS to incorporate logical operators into the standard handlebars.js conditional operator? Something like this:

{{#if section1 || section2}}
.. content
{{/if}}

I know I could write my own helper, but first I'd like to make sure I'm not reinventing the wheel.

Answer 1

This is possible by 'cheating' with a block helper. This probably goes against the Ideology of the people who developed Handlebars.

Handlebars.registerHelper('ifCond', function(v1, v2, options) {
  if(v1 === v2) {
    return options.fn(this);
  }
  return options.inverse(this);
});

You can then call the helper in the template like this

{{#ifCond v1 v2}}
    {{v1}} is equal to {{v2}}
{{else}}
    {{v1}} is not equal to {{v2}}
{{/ifCond}}

Answer 2

Taking the solution one step further. This adds the compare operator.

Handlebars.registerHelper('ifCond', function (v1, operator, v2, options) {

    switch (operator) {
        case '==':
            return (v1 == v2) ? options.fn(this) : options.inverse(this);
        case '===':
            return (v1 === v2) ? options.fn(this) : options.inverse(this);
        case '!=':
            return (v1 != v2) ? options.fn(this) : options.inverse(this);
        case '!==':
            return (v1 !== v2) ? options.fn(this) : options.inverse(this);
        case '<':
            return (v1 < v2) ? options.fn(this) : options.inverse(this);
        case '<=':
            return (v1 <= v2) ? options.fn(this) : options.inverse(this);
        case '>':
            return (v1 > v2) ? options.fn(this) : options.inverse(this);
        case '>=':
            return (v1 >= v2) ? options.fn(this) : options.inverse(this);
        case '&&':
            return (v1 && v2) ? options.fn(this) : options.inverse(this);
        case '||':
            return (v1 || v2) ? options.fn(this) : options.inverse(this);
        default:
            return options.inverse(this);
    }
});

Use it in a template like this:

{{#ifCond var1 '==' var2}}

Coffee Script version

Handlebars.registerHelper 'ifCond', (v1, operator, v2, options) ->
    switch operator
        when '==', '===', 'is'
            return if v1 is v2 then options.fn this else options.inverse this
        when '!=', '!=='
            return if v1 != v2 then options.fn this else options.inverse this
        when '<'
            return if v1 < v2 then options.fn this else options.inverse this
        when '<='
            return if v1 <= v2 then options.fn this else options.inverse this
        when '>'
            return if v1 > v2 then options.fn this else options.inverse this
        when '>='
            return if v1 >= v2 then options.fn this else options.inverse this
        when '&&', 'and'
            return if v1 and v2 then options.fn this else options.inverse this
        when '||', 'or'
            return if v1 or v2 then options.fn this else options.inverse this
        else
            return options.inverse this

Answer 3

Handlebars supports nested operations. This provides a lot of flexibility (and cleaner code) if we write our logic a little differently.

{{#if (or section1 section2)}}
.. content
{{/if}}

In fact, we can add all sorts of logic:

{{#if (or 
        (eq section1 "foo")
        (ne section2 "bar"))}}
.. content
{{/if}}

Just register these helpers:

Handlebars.registerHelper({
    eq: (v1, v2) => v1 === v2,
    ne: (v1, v2) => v1 !== v2,
    lt: (v1, v2) => v1 < v2,
    gt: (v1, v2) => v1 > v2,
    lte: (v1, v2) => v1 <= v2,
    gte: (v1, v2) => v1 >= v2,
    and() {
        return Array.prototype.every.call(arguments, Boolean);
    },
    or() {
        return Array.prototype.slice.call(arguments, 0, -1).some(Boolean);
    }
});

Answer 4

taking this one up a notch, for those of you who live on the edge.

gist : https://gist.github.com/akhoury/9118682 Demo : Code snippet below

Handlebars Helper: {{#xif EXPRESSION}} {{else}} {{/xif}}

a helper to execute an IF statement with any expression

1. EXPRESSION is a properly escaped String
2. Yes you NEED to properly escape the string literals or just alternate single and double quotes
3. you can access any global function or property ie encodeURIComponent(property)
4. this example assumes you passed this context to your handlebars template( {name: 'Sam', age: '20' } ) , notice age is a string , just for so I can demo parseInt() later in this post

Usage:

<p>
 {{#xif " name == 'Sam' && age === '12' " }}
   BOOM
 {{else}}
   BAMM
 {{/xif}}
</p>

Output

<p>
  BOOM
</p>

JavaScript: (it depends on another helper- keep reading)

 Handlebars.registerHelper("xif", function (expression, options) {
    return Handlebars.helpers["x"].apply(this, [expression, options]) ? options.fn(this) : options.inverse(this);
  });

Handlebars Helper: {{x EXPRESSION}}

A helper to execute javascript expressions

1. EXPRESSION is a properly escaped String
2. Yes you NEED to properly escape the string literals or just alternate single and double quotes
3. you can access any global function or property ie parseInt(property)
4. this example assumes you passed this context to your handlebars template( {name: 'Sam', age: '20' } ) , age is a string for demo purpose, it can be anything..

Usage:

<p>Url: {{x "'hi' + name + ', ' + window.location.href + ' <---- this is your href,' + ' your Age is:' + parseInt(this.age, 10)"}}</p>

Output:

<p>Url: hi Sam, http://example.com <---- this is your href, your Age is: 20</p>

JavaScript:

This looks a little large because I expanded syntax and commented over almost each line for clarity purposes

 Handlebars.registerHelper("x", function(expression, options) { var result; // you can change the context, or merge it with options.data, options.hash var context = this; // yup, i use 'with' here to expose the context's properties as block variables // you don't need to do {{x 'this.age + 2'}} // but you can also do {{x 'age + 2'}} // HOWEVER including an UNINITIALIZED var in a expression will return undefined as the result. with(context) { result = (function() { try { return eval(expression); } catch (e) { console.warn('•Expression: {{x \\'' + expression + '\\'}}\\n•JS-Error: ', e, '\\n•Context: ', context); } }).call(context); // to make eval's lexical this=context } return result; }); Handlebars.registerHelper("xif", function(expression, options) { return Handlebars.helpers["x"].apply(this, [expression, options]) ? options.fn(this) : options.inverse(this); }); var data = [{ firstName: 'Joan', age: '21', email: 'joan@aaa.bbb' }, { firstName: 'Sam', age: '18', email: 'sam@aaa.bbb' }, { firstName: 'Perter', lastName: 'Smith', age: '25', email: 'joseph@aaa.bbb' }]; var source = $("#template").html(); var template = Handlebars.compile(source); $("#main").html(template(data));

 h1 { font-size: large; } .content { padding: 10px; } .person { padding: 5px; margin: 5px; border: 1px solid grey; }

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script> <script src="http://cdnjs.cloudflare.com/ajax/libs/handlebars.js/1.0.0/handlebars.min.js"></script> <script id="template" type="text/x-handlebars-template"> <div class="content"> {{#each this}} <div class="person"> <h1>{{x "'Hi ' + firstName"}}, {{x 'lastName'}}</h1> <div>{{x '"you were born in " + ((new Date()).getFullYear() - parseInt(this.age, 10)) '}}</div> {{#xif 'parseInt(age) >= 21'}} login here: <a href="http://foo.bar?email={{x 'encodeURIComponent(email)'}}"> http://foo.bar?email={{x 'encodeURIComponent(email)'}} </a> {{else}} Please go back when you grow up. {{/xif}} </div> {{/each}} </div> </script> <div id="main"></div>

Moar

if you want access upper level scope, this one is slightly different, the expression is the JOIN of all arguments, usage: say context data looks like this:

// data
{name: 'Sam', age: '20', address: { city: 'yomomaz' } }

// in template
// notice how the expression wrap all the string with quotes, and even the variables
// as they will become strings by the time they hit the helper
// play with it, you will immediately see the errored expressions and figure it out

{{#with address}}
    {{z '"hi " + "' ../this.name '" + " you live with " + "' city '"' }}
{{/with}}

Javascript:

Handlebars.registerHelper("z", function () {
    var options = arguments[arguments.length - 1]
    delete arguments[arguments.length - 1];
    return Handlebars.helpers["x"].apply(this, [Array.prototype.slice.call(arguments, 0).join(''), options]);
});

Handlebars.registerHelper("zif", function () {
    var options = arguments[arguments.length - 1]
    delete arguments[arguments.length - 1];
    return Handlebars.helpers["x"].apply(this, [Array.prototype.slice.call(arguments, 0).join(''), options]) ? options.fn(this) : options.inverse(this);
});

Answer 5

There is a simple way of doing this without writing a helper function... It can be done within the template completely.

{{#if cond1}}   
  {{#if con2}}   
    <div> and condition completed</div>  
  {{/if}}
{{else}}   
  <div> both conditions weren't true</div>  
{{/if}}

Edit: Conversely you can do or's by doing this:

{{#if cond1}}  
  <div> or condition completed</div>    
{{else}}   
  {{#if cond2}}  
    <div> or condition completed</div>  
  {{else}}      
    <div> neither of the conditions were true</div>    
  {{/if}}  
{{/if}}

Edit/Note: From the handlebar's website: handlebarsjs.com here are the falsy values:

You can use the if helper to conditionally render a block. If its argument returns false, undefined, null, "" or [] (a "falsy" value), Then any 'cond' (like cond1 or cond2) will not be counted as true.

Answer 6

One problem with all of the answers posted here is that they don't work with bound properties, ie the if condition is not re-evaluated when the properties involved change. Here's a slightly more advanced version of the helper supporting bindings. It uses the bind function from the Ember source, which is also used to implement the normal Ember #if helper.

This one is limited to a single bound property on the left-hand side, comparing to a constant on the right-hand side, which I think is good enough for most practical purposes. If you need something more advanced than a simple comparison, then perhaps it would be good to start declaring some computed properties and using the normal #if helper instead.

Ember.Handlebars.registerHelper('ifeq', function(a, b, options) {
  return Ember.Handlebars.bind.call(options.contexts[0], a, options, true, function(result) {
    return result === b;
  });
});

You can use it like this:

{{#ifeq obj.some.property "something"}}
  They are equal!
{{/ifeq}}

Answer 7

Improved solution that basically work with any binary operator (at least numbers, strings doesn't work well with eval, TAKE CARE OF POSSIBLE SCRIPT INJECTION IF USING A NON DEFINED OPERATOR WITH USER INPUTS):

Handlebars.registerHelper("ifCond",function(v1,operator,v2,options) {
    switch (operator)
    {
        case "==":
            return (v1==v2)?options.fn(this):options.inverse(this);

        case "!=":
            return (v1!=v2)?options.fn(this):options.inverse(this);

        case "===":
            return (v1===v2)?options.fn(this):options.inverse(this);

        case "!==":
            return (v1!==v2)?options.fn(this):options.inverse(this);

        case "&&":
            return (v1&&v2)?options.fn(this):options.inverse(this);

        case "||":
            return (v1||v2)?options.fn(this):options.inverse(this);

        case "<":
            return (v1<v2)?options.fn(this):options.inverse(this);

        case "<=":
            return (v1<=v2)?options.fn(this):options.inverse(this);

        case ">":
            return (v1>v2)?options.fn(this):options.inverse(this);

        case ">=":
         return (v1>=v2)?options.fn(this):options.inverse(this);

        default:
            return eval(""+v1+operator+v2)?options.fn(this):options.inverse(this);
    }
});

Answer 8

Here's a solution if you want to check multiple conditions:

/* Handler to check multiple conditions
   */
  Handlebars.registerHelper('checkIf', function (v1,o1,v2,mainOperator,v3,o2,v4,options) {
      var operators = {
           '==': function(a, b){ return a==b},
           '===': function(a, b){ return a===b},
           '!=': function(a, b){ return a!=b},
           '!==': function(a, b){ return a!==b},
           '<': function(a, b){ return a<b},
           '<=': function(a, b){ return a<=b},
           '>': function(a, b){ return a>b},
           '>=': function(a, b){ return a>=b},
           '&&': function(a, b){ return a&&b},
           '||': function(a, b){ return a||b},
        }
      var a1 = operators[o1](v1,v2);
      var a2 = operators[o2](v3,v4);
      var isTrue = operators[mainOperator](a1, a2);
      return isTrue ? options.fn(this) : options.inverse(this);
  });

Usage:

/* if(list.length>0 && public){}*/

{{#checkIf list.length '>' 0 '&&' public '==' true}} <p>condition satisfied</p>{{/checkIf}}

Answer 9

Here's a link to the block helper I use: comparison block helper . It supports all the standard operators and lets you write code as shown below. It's really quite handy.

{{#compare Database.Tables.Count ">" 5}}
There are more than 5 tables
{{/compare}}

Answer 10

Similar to Jim's answer but a using a bit of creativity we could also do something like this:

Handlebars.registerHelper( "compare", function( v1, op, v2, options ) {

  var c = {
    "eq": function( v1, v2 ) {
      return v1 == v2;
    },
    "neq": function( v1, v2 ) {
      return v1 != v2;
    },
    ...
  }

  if( Object.prototype.hasOwnProperty.call( c, op ) ) {
    return c[ op ].call( this, v1, v2 ) ? options.fn( this ) : options.inverse( this );
  }
  return options.inverse( this );
} );

Then to use it we get something like:

{{#compare numberone "eq" numbretwo}}
  do something
{{else}}
  do something else
{{/compare}}

I would suggest moving the object out of the function for better performance but otherwise you can add any compare function you want, including "and" and "or".

Answer 11

Install Ember Truth Helpers addon by running the below command

ember install ember-truth-helpers

you can start use most of the logical operators(eq,not-eq,not,and,or,gt,gte,lt,lte,xor).

{{#if (or section1 section2)}}  
...content  
{{/if}}

You can even include subexpression to go further,

{{#if (or (eq section1 "section1") (eq section2 "section2") ) }}  
...content  
{{/if}}

Answer 12

Yet another crooked solution for a ternary helper:

'?:' ( condition, first, second ) {
  return condition ? first : second;
}

<span>{{?: fooExists 'found it' 'nope, sorry'}}</span>

Or a simple coalesce helper:

'??' ( first, second ) {
  return first ? first : second;
}

<span>{{?? foo bar}}</span>

Since these characters don't have a special meaning in handlebars markup, you're free to use them for helper names.

Answer 13

One other alternative is to use function name in #if . The #if will detect if the parameter is function and if it is then it will call it and use its return for truthyness check. Below myFunction gets current context as this .

{{#if myFunction}}
  I'm Happy!
{{/if}}

Answer 14

Unfortunately none of these solutions solve the problem of "OR" operator "cond1 || cond2".

1. Check if first value is true

2. Use "^" (or) and check if otherwise cond2 is true

   {{#if cond1}} DO THE ACTION {{^}} {{#if cond2}} DO THE ACTION {{/if}} {{/if}}

It breaks DRY rule. So why not use partial to make it less messy

{{#if cond1}}
    {{> subTemplate}}
{{^}}
    {{#if cond2}}
        {{> subTemplate}}
    {{/if}}
{{/if}}

Answer 15

I can understand why you would want to create a helper for situations where you have a large number of varied comparisons to perform within your template, but for a relatively small number of comparisons (or even one, which was what brought me to this page in the first place), it would probably just be easier to define a new handlebars variable in your view-rendering function call, like:

Pass to handlebars on render:

var context= {
    'section1' : section1,
    'section2' : section2,
    'section1or2' : (section1)||(section2)
};

and then within your handlebars template:

{{#if section1or2}}
    .. content
{{/if}}

I mention this for simplicity's sake, and also because it's an answer that may be quick and helpful while still complying with the logicless nature of Handlebars.

Answer 16

I have found a npm package made with CoffeeScript that has a lot of incredible useful helpers for Handlebars. Take a look of the documentation in the following URL:

https://npmjs.org/package/handlebars-helpers

You can do a wget http://registry.npmjs.org/handlebars-helpers/-/handlebars-helpers-0.2.6.tgz to download them and see the contents of the package.

You will be abled to do things like {{#is number 5}} or {{formatDate date "%m/%d/%Y"}}

Answer 17

if you just want to check if one or the other element are present you can use this custom helper

Handlebars.registerHelper('if_or', function(elem1, elem2, options) {
  if (Handlebars.Utils.isEmpty(elem1) && Handlebars.Utils.isEmpty(elem2)) {
    return options.inverse(this);
  } else {
    return options.fn(this);
  }
});

like this

{{#if_or elem1 elem2}}
  {{elem1}} or {{elem2}} are present
{{else}}
  not present
{{/if_or}}

if you also need to be able to have an "or" to compare function return values I would rather add another property that returns the desired result.

The templates should be logicless after all!

Answer 18

For those having problems comparing object properties, inside the helper add this solution

Ember.js helper not properly recognizing a parameter

Answer 19

Here we have vanilla handlebars for multiple logical && and ||(and or):

Handlebars.registerHelper("and",function() {
    var args = Array.prototype.slice.call(arguments);
    var options = args[args.length-1];

    for(var i=0; i<args.length-1; i++){
        if( !args[i] ){
            return options.inverse(this);
        }
    }

    return options.fn(this);
});


Handlebars.registerHelper("or",function() {
    var args = Array.prototype.slice.call(arguments);
    var options = args[args.length-1];

    for(var i=0; i<args.length-1; i++){
        if( args[i] ){
            return options.fn(this);
        }
    }

    return options.inverse(this);
}

// Results
// {{#and foo bar sally bob}} yup {{else}} nope {{/and}} // yup
// {{#or foo bar "" sally bob}} yup {{else}} nope {{/or}} // yup

// {{#and foo bar "" sally bob}} yup {{else}} nope {{/and}} // nope
// {{#or "" "" "" "" ""}} yup {{else}} nope {{/or}} // nope

Not so sure if it's "safe" to use "and" and "or"... maybe change to something like "op_and" and "op_or"?

Answer 20

Just came to this post from a google search on how to check if a string equals another string.

I use HandlebarsJS in NodeJS server-side, but I also use the same template files on the front-end using the browser version of HandlebarsJS to parse it. This meant that if I wanted a custom helper, I'd have to define it in 2 separate places, or assign a function to the object in question - too much effort!!

What people forget is that certain objects have inherit functions that can be used in the moustache template. In the case of a string:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match

An Array containing the entire match result and any parentheses-captured matched results; null if there were no matches.

We can use this method to return either an array of matches, or null if no matches were found. This is perfect, because looking at the HandlebarsJS documentation http://handlebarsjs.com/builtin_helpers.html

You can use the if helper to conditionally render a block. If its argument returns false, undefined, null, "", 0, or [], Handlebars will not render the block.

So...

{{#if your_string.match "what_youre_looking_for"}} 
String found :)
{{else}}
No match found :(
{{/if}}

UPDATE:

After testing on all browsers, this doesn't work on Firefox . HandlebarsJS passes other arguments to a function call, meaning that when String.prototype.match is called, the second argument (ie the Regexp flags for the match function call as per above documentation) appears to be being passed. Firefox sees this as a deprecated use of String.prototype.match, and so breaks.

A workaround is to declare a new functional prototype for the String JS object , and use that instead:

if(typeof String.includes !== 'function') {
    String.prototype.includes = function(str) {
        if(!(str instanceof RegExp))
            str = new RegExp((str+'').escapeRegExp(),'g');
        return str.test(this);
    }
}

Ensure this JS code is included before you run your Handlebars.compile() function, then in your template...

{{#your_string}}
    {{#if (includes "what_youre_looking_for")}} 
        String found :)
    {{else}}
        No match found :(
    {{/if}}
{{/your_string}}

Answer 21

You can do it simply by using the logical operator like this shown below:

{{#if (or(eq firstValue 'String_to_compare_value') (eq secondValue 'String_to_compare_value'))}}business logic goes here{{/if}}

{{#if (and(eq firstValue 'String_to_compare_value') (eq secondValue 'String_to_compare_value'))}}business logic goes here{{/if}}

Before closing if you can write your business logic

Answer 22

Correct Solution for AND/OR

Handlebars.registerHelper('and', function () {
    // Get function args and remove last one (function name)
    return Array.prototype.slice.call(arguments, 0, arguments.length - 1).every(Boolean);
});
Handlebars.registerHelper('or', function () {
    // Get function args and remove last one (function name)
    return Array.prototype.slice.call(arguments, 0, arguments.length - 1).some(Boolean);
}); 

Then call as follows

{{#if (or (eq questionType 'STARTTIME') (eq questionType 'ENDTIME') (..) ) }}

BTW: Note that the solution given here is incorrect, he's not subtracting the last argument which is the function name. https://stackoverflow.com/a/31632215/1005607

His original AND/OR was based on the full list of arguments

   and: function () {
        return Array.prototype.slice.call(arguments).every(Boolean);
    },
    or: function () {
        return Array.prototype.slice.call(arguments).some(Boolean);
    }

Can someone change that answer? I just wasted an hour trying to fix something in an answer recommended by 86 people. The fix is to filter out the last argument which is the function name. Array.prototype.slice.call(arguments, 0, arguments.length - 1)

Answer 23

Following these 2 guides a-way-to-let-users-define-custom-made-bound-if-statements and custom bound helpers I was able to adjust my shared views in this post on stackoverflow to use this instead of the standard #if statement. This should be more secure than just tossing an #if in there.

The custom bound helpers in that gist are outstanding.

<li>
    <a href="{{unbound view.varProductSocialBlog}}">
        {{#if-equal view.showDiv "true"}}<div>{{/if-equal}}<i class="fa fa-rss-square"></i>{{#if-equal view.showDiv "true"}}</div>{{/if-equal}}
        {{#if-equal view.showTitle "true"}}Blog{{/if-equal}}
    </a>
</li>

I am using the ember cli project to build my ember application.

Current setup at the time of this post:

DEBUG: -------------------------------
DEBUG: Ember      : 1.5.1
DEBUG: Ember Data : 1.0.0-beta.7+canary.b45e23ba
DEBUG: Handlebars : 1.3.0
DEBUG: jQuery     : 2.1.1
DEBUG: -------------------------------

Answer 24

In Ember.js you can use inline if helper in if block helper. It can replace || logical operator, for example:

{{#if (if firstCondition firstCondition secondCondition)}}
  (firstCondition || (or) secondCondition) === true
{{/if}}

Answer 25

You can use the following code:

{{#if selection1}}
    doSomething1
{{else}}
   {{#if selection2}}
       doSomething2
   {{/if}}
{{/if}}

Answer 26

you cannot write your expressions inside handlebars template but all of your logic (expressions) in express.js

res.render("view.hbs", {expression: section1 || section2})

Answer 27

Here's an approach I'm using for ember 1.10 and ember-cli 2.0.

// app/helpers/js-x.js
export default Ember.HTMLBars.makeBoundHelper(function (params) {
  var paramNames = params.slice(1).map(function(val, idx) { return "p" + idx; });
  var func = Function.apply(this, paramNames.concat("return " + params[0] + ";"))
  return func.apply(params[1] === undefined ? this : params[1], params.slice(1));
});

Then you can use it in your templates like this:

// used as sub-expression
{{#each item in model}}
  {{#if (js-x "this.section1 || this.section2" item)}}
  {{/if}}
{{/each}}

// used normally
{{js-x "p0 || p1" model.name model.offer.name}}

Where the arguments to the expression are passed in as p0 , p1 , p2 etc and p0 can also be referenced as this .