Typeguards enable us to process function arguments based on their types. Consider this example - 1 2 3 4 5 function join(a: string): string { return a; } console.log(join("hello")); // hello What if we want to use join for strings or numbers? We can do a union type like so -

Typescript provides a convenient way to accept different types of arguments for a function, or to combine multiple types into one super type. Consider this example - 1 2 3 4 5 function printThis(a: string) { return typeof a; } console.log(printThis("hello")); // string This function is fine if we want to return the input string for some strange reason.

Overload functions to change signatures and provide optional arguments in Typescript. We have previously seen an option to provide optional arguments to a function in Typescript. But, there is more to that to function overloads. Building on our previous example - 1 2 3 4 5 6 7 8 function getSum(i: number, j?

Let us discuss everyone’s favourite topic since Typescript was invented - ‘duck typing’. Duck typing is type safety checks for complex types. It gets its name following the adage - If it walks like a duck and quacks like a duck, it must be a duck. Typescript modifies it slightly to -

Allow additional arguments or optional arguments for function calls in Typescript. Consider the below example of a function that adds two numbers. 1 2 3 4 5 6 function getSum(i: number, j: number): number { return i + j; } console.log(getSum(1, 2)); // 3 This works fine and as expected, but what happens when there is a discrepancy in number of arguments.

Beware of using implicit returns in arrow functions. Consider the below example of a simple arrow function. It returns a simple variable. In the absence of any other statement in the function body, a simple mention of x will return the value of x. 1 2 3 const getStuff = x => x; console.

Are public and private variables really public or private? Consider the below example - 1 2 3 4 5 6 7 class MathOp { public x: number; private y: number; } const op = new MathOp(); op.x; // no problem If you try to access the private variable.

With ‘type’ in its name, Typescript lives up to its reputation of being a typed language. But, what exactly are the supported types? At a high-level we can classify types as built-in (basic & special ) and additional types including user-defined types. Built-in Types (Basic) Similar to Javascript implicit types, we have number, string, boolean to form the three core built-in types.

Use onclick rather than submit in HTML forms. A typical HTML form has a few fields and a button to submit the data to some back-end server. And, the typical way to do the form submission is through the submit method. 1 2 3 4 5 <form action="/helloMessage.php"> <input type="text" id="name" /><br /> <button type="submit"></button> </form> On clicking the button, the page will submit data to helloMessage.

Get started with object oriented programming in Typescript. Typescript behaves like a language with built-in support for OOP concepts, and does not carry the quirks of Javascript in that respect. Classes and Objects Define classes and objects like how you define in any of the popular OOP languages. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 class Fruit { public name: string; private grownIn: Array<string>; constructor(name: string, grownIn: Array<string>) { this.

I had been fascinated by Typescript and have been going back and forth on making it my primary programming language. In a few posts and with as much less information as possible, let’s see why anyone should bother with Typescript. What is Typescript? Typescript is a typed Javascript. No, I am kidding - it is more than that.

How can you use await without an async function? Don’t click or proceed further if you are not into practical jokes. Say, you try using await in a “normal” function or directly within a module.. 1 2 3 4 5 6 7 function getWeather(loc) { const weather = await fetchWeather(loc); return weather; } // SyntaxError: await is only valid in async function You receive a compilation error that await can be used only in async function.

Generate Fibonacci series with generators and feel good about yourself. Previously you have seen how the totally practical example of generating Fibonacci series was breathing fire with memoization, and may have also come across using loops or recursion to solve the same problem. But, there is no fun in all that - this is real-life and we have to “generate” fun (yep, there we go again).