In the confusing jungle of transpiler languages for JavaScript, there are some gems. TypeScript is mainstream, ReScript is starting to establish itself, and Elm is still an insider tip. This article takes a detailed look at ReScript – but also sheds light on the limitations of the young language. In what projects does its use make sense? What projects should rather use TypeScript on the one hand or Elm on the other?
We’ve got a lot of great features in TypeScript 3.7, including:
Optional Chaining
Nullish Coalescing
Assertion Functions
Better Support for never-Returning Functions
--declaration and --allowJs
(More) Recursive Type Aliases
The useDefineForClassFields Flag and The declare Property Modifier
Build-Free Editing with Project References
Uncalled Function Checks
Flatter Error Reporting
// @ts-nocheck in TypeScript Files
Semicolon Formatter Option
Website and Playground Updates
Breaking Changes
DOM Changes
Class Field Mitigations
Function Truthy Checks
Local and Imported Type Declarations Now Conflict
API Changes
This project uses mocha, chai, typescript and vs code debug toghether, so you can write your api tests easily.
This is useful for scenarios when you've some api developed in python for example, but you'd prefer to develop tests in typescript/javascript.
Another use case is when you've some legacy api and you want to develop some tests to make [risk free change] of your legacy api possibel!
JavaScript and TypeScript support enhancements include a reworked Rename refactoring (which can now rename files corresponding to TypeScript types), granular formatter settings, and full support for TypeScript 1.8.
npm install -g typescript@2.0
<TypeScriptToolsVersion>2.0</TypeScriptToolsVersion>
using System;
namespace EFCoreDbFunctionsSample.Entities
{
public class Person
{
public int Id { get; set; }
public string Name { get; set; }
public DateTime AddDate { get; set; }
}
} var usersInfo = context.People.Where(person => (DateTime.Now - person.AddDate).Days <= 10).ToList();
'The LINQ expression 'DbSet<Person>.Where(p => (DateTime.Now - p.AddDate).Days <= 10)' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.'
SELECT [p].[Id], [p].[AddDate], [p].[Name] FROM [People] AS [p] WHERE DATEDIFF(Day, [p].[AddDate], GETDATE()) <= 10
namespace EFCoreDbFunctionsSample.DataLayer
{
public enum SqlDateDiff
{
Year,
Quarter,
Month,
DayOfYear,
Day,
Week,
Hour,
Minute,
Second,
MilliSecond,
MicroSecond,
NanoSecond
}
public static class SqlDbFunctionsExtensions
{
public static int SqlDateDiff(SqlDateDiff interval, DateTime initial, DateTime end)
=> throw new InvalidOperationException($"{nameof(SqlDateDiff)} method cannot be called from the client side.");
public static readonly MethodInfo SqlDateDiffMethodInfo = typeof(SqlDbFunctionsExtensions)
.GetRuntimeMethod(
nameof(SqlDbFunctionsExtensions.SqlDateDiff),
new[] { typeof(SqlDateDiff), typeof(DateTime), typeof(DateTime) }
);
}
} namespace EFCoreDbFunctionsSample.DataLayer
{
public class ApplicationDbContext : DbContext
{
// ...
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.HasDbFunction(SqlDbFunctionsExtensions.SqlDateDiffMethodInfo)
.HasTranslation(args =>
{
var parameters = args.ToArray();
var param0 = ((SqlConstantExpression)parameters[0]).Value.ToString();
return SqlFunctionExpression.Create("DATEDIFF",
new[]
{
new SqlFragmentExpression(param0), // It should be written as DateDiff(day, ...) and not DateDiff(N'day', ...) .
parameters[1],
parameters[2]
},
SqlDbFunctionsExtensions.SqlDateDiffMethodInfo.ReturnType,
typeMapping: null);
});
}
}
} var sinceDays = 10;
users = context.People.Where(person =>
SqlDbFunctionsExtensions.SqlDateDiff(SqlDateDiff.Day, person.AddDate, DateTime.Now) <= sinceDays).ToList();
/*
SELECT [p].[Id], [p].[AddDate], [p].[Name]
FROM [People] AS [p]
WHERE DATEDIFF(Day, [p].[AddDate], GETDATE()) <= @__sinceDays_0
*/ npm WARN engine rxjs@5.0.0-beta.6: wanted: {"npm":">=2.0.0"} (current: {"node":"v0.10.31","npm":"1.4.9"}) 
{
"name": "asp-net-mvc5x-angular2x",
"version": "1.0.0",
"author": "DNT",
"description": "",
"scripts": {},
"license": "Apache-2.0",
"dependencies": {
"jquery": "2.2.3",
"angular2": "2.0.0-beta.15",
"systemjs": "^0.19.26",
"es6-promise": "^3.1.2",
"es6-shim": "^0.35.0",
"reflect-metadata": "0.1.2",
"rxjs": "5.0.0-beta.2",
"zone.js": "^0.6.12",
"bootstrap": "^3.3.6"
},
"devDependencies": {
"typescript": "^1.8.9",
"typings": "^0.8.1"
},
"repository": {
}
} 
{
"compileOnSave": true,
"compilerOptions": {
"target": "es5",
"module": "system",
"moduleResolution": "node",
"noImplicitAny": false,
"noEmitOnError": true,
"removeComments": false,
"sourceMap": true,
"emitDecoratorMetadata": true,
"experimentalDecorators": true
},
"exclude": [
"node_modules",
"wwwroot",
"typings/main",
"typings/main.d.ts"
]
} 8 Tips for Clean TypeScript Code you Must Know
