Typescript (Javascript) Cheat Sheet

1. Falsy values
false — boolean false
0 — number zero
“” — empty string
null
undefined
NaN — Not A Number

2. Immutability conversion
mutable:
this.currentUser.classes.push(classId);

immutable:
this.currentUser = Object.assign({}, this.currentUser,
     {classes: this.currentUser.classes.concat([classId])});

mutable:
user.classes = user.classes || [];
this.currentUser = user;

immutable:
this.currentUser = Object.assign({}, user,
     {classes: user.classes || []});

How to make Rails Turbolinks play nicely with jQuery

On Rails 4, AJAX in my pages are not being called because of turbolinks. The solution is to wrap the javascript code around the page load event. Got this solution from this post.

What works for me is this…

var ready = function() {
  ...your javascript goes here...
};

$(document).ready(ready);
$(document).on('page:load', ready);

Client-Side Validation for a Custom DataAnnonation in MVC 4

This is a continuation of my previous post. This is based from this excellent tutorial.

First step is to implement IClientValidatable interface in the FileTypesAttribute class:

public class FileTypesAttribute : ValidationAttribute, IClientValidatable {
        private readonly List _types;
        private readonly string specifiedTypes;

        public FileTypesAttribute(string types) {
            _types = types.Split(',').ToList();
            specifiedTypes = types;
        }

        public override bool IsValid(object value) {
            if (value == null) return true;
            var postedFile = value as HttpPostedFileBase;
            var fileExt = System.IO.Path.GetExtension(postedFile.FileName).Substring(1);
            return _types.Contains(fileExt, StringComparer.OrdinalIgnoreCase);
        }

        public override string FormatErrorMessage(string name) {
            return string.Format("Invalid file type. Only {0} are supported.", String.Join(", ", _types));
        }

        public IEnumerable GetClientValidationRules(ModelMetadata metadata, ControllerContext context) {
            var rule = new ModelClientValidationRule();
            rule.ErrorMessage = FormatErrorMessage(metadata.GetDisplayName());
            rule.ValidationType = "filetypes";
            rule.ValidationParameters.Add("types", specifiedTypes);
            yield return rule;
        }
    }

Things to note here are the validationtype="filetypes" and the added parameter="types", which can be observed in the emitted html below:

<input data-val="true" data-val-filetypes="Invalid file type. Only xls, xlsx are supported."
data-val-filetypes-types="xls,xlsx" data-val-required="The AttachmentTrace field is required."
id="AttachmentTrace" name="AttachmentTrace" type="file" value="" />

The added parameter called types has a value of "xls,xlsx". This parameter and validationtype are significant because it will be used for the jquery validator and adapter as follows:

$(function () {
    // custom validation method
    $.validator.addMethod("filetypes",
        function (value, element, params) {
            if (value == null) return true;
            var fileExtension = value.split('.').pop().toLowerCase();
            var types = params.toLowerCase();
            return types.indexOf(fileExtension) !== -1;
        }
    );
    // add to unobtrusive adapters
    $.validator.unobtrusive.adapters.addSingleVal("filetypes", "types");
} (jQuery));

The value has the contents of the input element, while params has the parameter value of "xls,xlsx" from the data annotation.