How to add custom validator to paper-input?

Question

Need to add a custom validator which does some complex validation based on the values of other fields in the html.

Tried adding custom validator function as an attribute to the paper-input element but it wont get called at all.

    <dom-module id='custom-ele'>
            <paper-input is="iron-input" id='input_1' label='Label_1' validator='validate_1'></paper-input>
            <paper-input is="iron-input" id='input_2' label='Label_2' validator='validate_2'></paper-input>
            ...
    </dom-module>
    <script>
    Polymer({

        is: 'custom-ele',

        validate_1: function() {
            //validation code
        },

        validate_2: function() {
           //validation code 
        }

    });
    </script>

Answer 1

The validator has to implement IronValidatorBehavior (see docs). Also, if you want to validate automatically, you need to set the auto-validate attribute. To achieve your goal you could create a custom validator for each type of validation that you want to use. Alternatively, you could create a generic custom validator and set the validate function upon initialisation. Here's an example.

Polymer({

    is: 'custom-validator',

    behaviors: [
        Polymer.IronValidatorBehavior
    ]
});

<dom-module id='validation-element'>
    <template>
        <custom-validator id="valid1" validator-name="validator1"></custom-validator>
        <custom-validator id="valid2" validator-name="validator2"></custom-validator>
        <paper-input auto-validate id='input_1' label='Label_1' validator='validator1'></paper-input>
        <paper-input auto-validate id='input_2' label='Label_2' validator='validator2'></paper-input>
    </template>
</dom-module>
<script>

    Polymer({

        is: 'validation-element',

        validate1: function(value) {
            //validation code
            console.log("validate1");
            return value.length > 3;
        },

        validate2: function(value) {
            //validation code
            console.log("validate2");
            return value.length > 5;
        },

        ready: function() {
            this.$.valid1.validate = this.validate1.bind(this);
            this.$.valid2.validate = this.validate2.bind(this);
        }

    });

</script>

You can find a working example in this plunk.

Answer 2

Ok, my answer might not be the "Polymer way" but it works and is more the "traditional programmatic" way.

The short list of ideas for this solution:

1. paper-input aka iron-input look-up the value of the validator attribute in the iron-meta global object
2. Each Polymer.IronValidatorBehavior has a name (validatorName), a type ('validator') and a validate function
3. Each Polymer.IronValidatorBehavior registers itself in the corresponding 'validator' list in the iron-meta object

So this is a short code I derived from the points above:

var validator = {
    validatorName: 'my-custom-validator',
    validatorType: 'validator',
    validate:      function(value) { ...my validation code... }
};
new Polymer.IronMeta({
    type: validator.validatorType,
    key: validator.validatorName,
    value: validator
});

You can put this code in any 'attached' or 'created' event handler. But run it before any validation is done of course...

Then you can write

<paper-input validator="my-custom-validator"></paper-input>

If you wanna check if your validator is register with the input, navigate down the dom-tree in any dev-tool and hit: $0.hasValidator() and $0.validator to see if your validator has been successfully registered with the input.