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How do I render a Boolean to a JavaScript variable in a cshtml file?

Presently this shows a syntax error:

<script type="text/javascript" >

    var myViewModel = {
        isFollowing: @Model.IsFollowing  // This is a C# bool
    };
</script>

How do I render a Boolean to a JavaScript variable in a cshtml file?

Presently this shows a syntax error:

<script type="text/javascript" >

    var myViewModel = {
        isFollowing: @Model.IsFollowing  // This is a C# bool
    };
</script>

• javascript
• asp.net-mvc
• razor

Share Improve this question Follow edited Oct 27, 2017 at 11:39 Mafii 7,41511 gold badge3838 silver badges5656 bronze badges asked Jan 21, 2013 at 22:46 NikosNikos 7,55299 gold badges5757 silver badges9696 bronze badges 0

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7 Answers 7

Sorted by: Reset to default 363

You may also want to try:

isFollowing: '@(Model.IsFollowing)' === '@true'

and an ever better way is to use:

isFollowing: @Json.Encode(Model.IsFollowing)

Because a search brought me here: in ASP.NET Core, IJsonHelper doesn't have an Encode() method. Instead, use Serialize(). E.g.:

isFollowing: @Json.Serialize(Model.IsFollowing)    

The JSON boolean must be lowercase.

Therefore, try this (and make sure nto to have the // comment on the line):

var myViewModel = {
    isFollowing: @Model.IsFollowing.ToString().ToLower()
};

Or (note: you need to use the namespace System.Xml):

var myViewModel = {
    isFollowing: @XmlConvert.ToString(Model.IsFollowing)
};

var myViewModel = {
    isFollowing: '@(Model.IsFollowing)' == "True";
};

Why True and not true you ask... Good question:
Why does Boolean.ToString output "True" and not "true"

A solution which is easier to read would be to do this:

isFollowing: @(Model.IsFollowing ? "true" : "false")

Here's another option to consider, using the !! conversion to boolean.

isFollowing: !!(@Model.IsFollowing ? 1 : 0)

This will generate the following on the client side, with 1 being converted to true and 0 to false.

isFollowing: !!(1)  -- or !!(0)

Defining a conversion operation and adding an override of .ToString() can save a lot of work.

Define this struct in your project:

/// <summary>
/// A <see cref="bool"/> made for use in creating Razor pages.
/// When converted to a string, it returns "true" or "false".
/// </summary>
public struct JSBool
{
    private readonly bool _Data;

    /// <summary>
    /// While this creates a new JSBool, you can also implicitly convert between the two.
    /// </summary>
    public JSBool(bool b)
    {
        _Data = b;
    }

    public static implicit operator bool(JSBool j) => j._Data;
    public static implicit operator JSBool(bool b) => new JSBool(b);

    // Returns "true" or "false" as you would expect
    public override string ToString() => _Data.ToString().ToLowerInvariant();
}

Usage

You can directly cast a C# bool, as in the case of the question:

{
    // Results in `isFollowing : true`
    isFollowing : @((JSBool)Model.IsFollowing)
}

But you can also use a JSBool directly in the Razor code with the expectation that it will give true and false without having to do any extra work:

@{
    JSBool isA = true;
    JSBool isB = false;
    // Standard boolean operations work too:
    JSBool isC = a || b;
}

<script>
    if (@isC)
        console.log('true');
</script>

This works because of the implicit conversion operators we defined above.

---

Just make sure to only ever use this when you intend to use it in Razor code. In other words, don't use it with normal C# as this can make your code messy.

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