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can-form

Can-Form is a form component for the CanJS framework. It takes care of the form validation and error reporting while allowing you to do things the "CanJS way".

Notable features:

  • Form based validations (with support for nested objects)
  • Composable / nestable form
  • Error reporting
  • Intelligent validation management - validates only the fields that user changed, or all of them if the form is submitted
  • Behaves like a real form (pressing enter in the input field will submit the form)
  • Behaves like a Component (can.Component)

Form based validations

You can add validations to the form component by using the validate property:

FormComponent.extend({
    tag : 'simple-form',
    template : '<content><content>',
    validate : {
        username : [FormComponent.validationRules.presenceOf()],
        password : [FormComponent.validationRules.presenceOf()]
    }
});

This is a simple form example, that validates presence of username and password attributes.

You initialize it like this:

<simple-form map="{userModel}">
    <input type="text" can-value="username">
    <input type="text" can-value="password">
    <button>Submit</button>
</simple-form>

Context inside the form template will be set to whatever was passed in the map attribute of the form tag.

Form will automatically wrap your content in the form element so you shouldn't include it yourself.

Although the data will be validated, the errors will not be show. To show the errors, use the errors helper:

<simple-form map="{userModel}">
    <input type="text" can-value="username">
    {{#errors 'username'}}
        <ul class="bg-danger list-unstyled">
            {{#this}}
                <li>{{ . }}</li>
            {{/this}}
        </ul>
    {{/errors}}
    <input type="text" can-value="password">
    {{#errors 'password'}}
        <ul class="bg-danger list-unstyled">
            {{#this}}
                <li>{{ . }}</li>
            {{/this}}
        </ul>
    {{/errors}}
    <button>Submit</button>
</simple-form>

Now the errors will be shown whenever the user changes the input or submits the form.

Composable / nestable forms

When you have a nested data structure it can be tricky to keep track of your fields and errors - modelling the form after your data can be a pain.

can-form allows you to nest the form components one inside another. Let's say that you want add ability for your users to add their social network accounts in the form.

can-form comes with the default form component called form-for that can be used for cases like this:

<simple-form map="{userModel}">
    <input type="text" can-value="username">
    {{#errors 'username'}}
        <ul class="bg-danger list-unstyled">
            {{#this}}
                <li>{{ . }}</li>
            {{/this}}
        </ul>
    {{/errors}}
    <input type="text" can-value="password">
    {{#errors 'password'}}
        <ul class="bg-danger list-unstyled">
            {{#this}}
                <li>{{ . }}</li>
            {{/this}}
        </ul>
    {{/errors}}

    {{#each socialNetworks}}
        <form-for map="{this}" path="socialNetworks.{{@index}}">
            <input type="text" can-value="network">
            // error reporting code here
            <input type="text" can-value="username">
            // error reporting code here
        </form-for>
    {{/each}}
    <button>Submit</button>
</simple-form>

This might look a bit confusing at first so let me explain what happens here:

  • we itereate through all elements in the socialNetworks array
  • we create a new form-for element for each item in the array
  • we use the path attribute to hint what is the path from the parent context, this is needed for the error reporting and validations
  • finally we have our inputs, but these inputs include only the name of the attribute in the current context - this makes forms reusable

If we wanted to validate the socialNetworks array we can add the following to our component constructor:

FormComponent.extend({
    tag : 'simple-form',
    template : '<content><content>',
    validate : {
        username : [FormComponent.validationRules.presenceOf()],
        password : [FormComponent.validationRules.presenceOf()],
        'socialNetworks.*.username' : [FormComponent.validationRules.presenceOf()],
        'socialNetworks.*.network' : [FormComponent.validationRules.presenceOf()]
    }
});

When you use the socialNetworks.*.network syntax it sets up the validation for the network property of each item in the socialNetworks array (This syntax is based on the path syntax generated by the can.Map events);

Alternate approach

If we wanted to reuse the form component for the social network map, we could create it's own component:

FormComponent.extend({
    tag : 'social-network',
    template : socialNetworkTemplate,
    validate : {
        username : [FormComponent.validationRules.presenceOf()],
        network : [FormComponent.validationRules.presenceOf()]
    }
})

For the view we can just use the following code:

<input type="text" can-value="network">
{{#errors 'network'}}
    <ul class="bg-danger list-unstyled">
        {{#this}}
            <li>{{ . }}</li>
        {{/this}}
    </ul>
{{/errors}}
<input type="text" can-value="username">
{{#errors 'username'}}
    <ul class="bg-danger list-unstyled">
        {{#this}}
            <li>{{ . }}</li>
        {{/this}}
    </ul>
{{/errors}}

Now we can include the social-network component inside the simple-form:

<simple-form map="{userModel}">
    <input type="text" can-value="username">
    {{#errors 'username'}}
        <ul class="bg-danger list-unstyled">
            {{#this}}
                <li>{{ . }}</li>
            {{/this}}
        </ul>
    {{/errors}}
    <input type="text" can-value="password">
    {{#errors 'password'}}
        <ul class="bg-danger list-unstyled">
            {{#this}}
                <li>{{ . }}</li>
            {{/this}}
        </ul>
    {{/errors}}

    {{#each socialNetworks}}
        <social-network map="{this}" path="socialNetworks.{{@index}}">
        </social-network>
    {{/each}}
    <button>Submit</button>
</simple-form>

This approach allows you to reuse forms across different context while keeping the same validations and behavior.

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Form Library for CanJS

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