This is the archived version of Roland Weigelt's weblog that ran from 2003 to 2023 at weblogs.asp.net

Contents tagged with TypeScript

  • A Stupid Little TypeScript Mistake (Part 2)

    5 Comments

    After my blog post in June, here is another tale from a C# developer getting his feet wet with TypeScript.

    TypeScript’s type checking makes my life so much easier, but it does not catch everything. Recently I forgot an important part of a for-loop. Here is a stripped-down example:

    var items=["item0", "item1", "item2"];
for (var n=0;items.length;n++)
{
    // ...
}

    The code compiles, but runs into an endless loop – the “n<” is missing in the condition.

    If I write similar code in C#…

    var items=new[] {"item0", "item1", "item2"};
for (var n=0;items.Length;n++)
{
    // ...
}

    … the compiler tells me what I did wrong:

    Cannot implicitly convert type 'int' to 'bool'

    Ok, another (TypeScript) lesson learned.

  • A Stupid Little TypeScript Mistake

    4 Comments

    For context: I am a C# developer who uses TypeScript just every now and then. Recently I added a few string constants to an existing TypeScript class. The program compiled just fine, but when I ran the program, the result was different from what I expected.

    For a repro scenario, copy the following script code into the Windows clipboard:

    class MyStrings {
    public static LoremIpsumDolorSitAmet = "Lorem ipsum dolor sit amet";
    public static ConsecteturAdipiscingElit = "consectetur adipiscing elit";
    public static VestibulumFeugiatLigulaEuOdioPosuereVelTristiqueDiamIaculis = "Vestibulum feugiat ligula eu odio posuere, vel tristique diam iaculis";
    public static FusceUrnaLiberoEfficiturNecTortorSed = "Fusce urna libero, efficitur nec tortor sed";
    public static UllamcorperFaucibusAugueProinUtPurusMetus = "ullamcorper faucibus augue. Proin ut purus metus";
    public static CurabiturAPosuereDiamSedElementumSedNislVitaeMaximus = "Curabitur a posuere diam. Sed elementum sed nisl vitae maximus";
    public static PraesentVitaeEnimVestibulumUltriciesNuncInGravidaSapien = "Praesent vitae enim vestibulum, ultricies nunc in, gravida sapien";
    public static ProinIaculisMiOrciUtRhoncusDuiVenenatisId : "Proin iaculis mi orci, ut rhoncus dui venenatis id";
    public static MorbiSedCongueLigulaSedFinibusNeque : "Morbi sed congue ligula, sed finibus neque";
    public static PellentesqueEuMolestieExIdFermentumEllus : "Pellentesque eu molestie ex, id fermentum tellus";
}

console.log(MyStrings.LoremIpsumDolorSitAmet);
console.log(MyStrings.ConsecteturAdipiscingElit);
console.log(MyStrings.VestibulumFeugiatLigulaEuOdioPosuereVelTristiqueDiamIaculis);
console.log(MyStrings.FusceUrnaLiberoEfficiturNecTortorSed);
console.log(MyStrings.UllamcorperFaucibusAugueProinUtPurusMetus);
console.log(MyStrings.CurabiturAPosuereDiamSedElementumSedNislVitaeMaximus);
console.log(MyStrings.PraesentVitaeEnimVestibulumUltriciesNuncInGravidaSapien);
console.log(MyStrings.ProinIaculisMiOrciUtRhoncusDuiVenenatisId);
console.log(MyStrings.MorbiSedCongueLigulaSedFinibusNeque);
console.log(MyStrings.PellentesqueEuMolestieExIdFermentumEllus);

    Now head to the TypeScript Playground at https://www.typescriptlang.org/play, replace the text on the left side with the content of the clipboard and run the script.

    This will give you the following output:

    It took me a bit until it dawned on me why the last three strings are undefined – can you immediately figure out what the problem is?

    A hint: Just before I edited the class, I worked on a couple of JSON files.