Limit the length of a post being displayed in handlebars

Question

I have a blog app that I'm building for a class. It's an express app using sequelize and handlebars. I am able to display the most recent 4 plost on the home page and display all posts on the /post route, but I am trying to show only a limited number of characters with a read more.. buton that links to the full post. I cannot figure out how to limit the number of characters. I found some handlebars helpers on here but cannot get them to work.

Here is my partial:

<div class="container">
    {{#each posts as |post|}}

        <div class="card mt-4">
            <div class="card-header bg-dark">
                {{ post.title }}
                <div class="text-end">Submitted {{ format_date post.createdAt}}</div>
            </div>
            <div class="card-body text-dark">
                <h5 class="card-title">{{ User.username }}</h5>
                <p class="card-text">{{ post.body }}</p>
                <a href="/posts/{{ post.id}}" class="btn btn-dark">Read more...</a>
            </div>
        </div>
    {{/each}}
</div>

I have a helpers.js file to format the date but I cannot figure out how to incorporate a helper to trim the post length.

Here is my current helper.js file:

function getMonthName(val){
    switch(val){
        case 0 :
            return 'January';
        case 1 :
            return 'February';
        case 2 :
            return 'March';
        case 3 :
            return 'April';
        case 4 :
            return 'May';
        case 5 :
            return 'June';
        case 6 :
            return 'July';
        case 7 :
            return 'August';
        case 8 :
            return 'September';
        case 9 :
            return 'October';
        case 10 :
            return 'November';
        case 11 :
            return 'December';
        default:
            return '';
    }
}

module.exports = {
    format_date: date => {
        var hours = date.getHours();
        var minutes = date.getMinutes();
        var ampm = hours >= 12 ? 'pm' : 'am';
        hours = hours % 12;
        hours = hours ? hours : 12; // the hour '0' should be '12'
        minutes = minutes < 10 ? '0'+minutes : minutes;
        var strTime = hours + ':' + minutes + ' ' + ampm;
        let monthValue = date.getMonth();
        return (getMonthName(monthValue)) + " " + date.getDate() + ", " + date.getFullYear() + " at " + strTime;
        //return `${new Date(date).getMonth() + 1}/${new Date(date).getDate()}/${new Date(date).getFullYear()}`;
    }
}