Exploring Immediately Invoked Function Expressions in TypeScript

Question

Exploring Immediately Invoked Function Expressions in TypeScript

I came across an interesting article on self-invoking functions in JavaScript by Minko Gechev. This article teaches us how to create a JavaScript function that calls itself immediately after being initialized. I am curious about how we can achieve this in TypeScript. When I attempted to write the code within export class ComponentName, it did not work. Here's the code snippet I tried:

import {Component, Input} from '@angular/core'

@Component({...})

export class MyComponent{

    @Input() infoes;

    (function(){
        console.log('testing');
    })();
}

The IDE displayed an error stating

unexpected token. a constructor, accessor, method or property was expected

. I believe this error is related to the class concept introduced in TypeScript.

angular typescript

Answer 1

Answer №1

In TypeScript, an IIFE (immediately-invoked function expression) can only be used in places where expressions are allowed. Isolated expressions are not permitted in TypeScript. For example, you cannot have something like `class Foo { 1+1; };`. However, using an IIFE to initialize a field is allowed, as shown in the following example:

class Foo {
    foo: string = (function bar(){
        console.log("testing");
        return "value";
    }());
};

new Foo();

If you run the above code, you will see `testing` printed on the console.

It's also important to note that you cannot define a function inside a class like this:

class Foo {
    function bar(){
        console.log('testing');
    );
}

The correct way to define a method in a class is illustrated below:

class Foo {
    bar(){
        console.log('testing');
    );
}

Answer 2

In TypeScript, an IIFE (immediately-invoked function expression) can only be used in places where expressions are allowed. Isolated expressions are not permitted in TypeScript. For example, you cannot have something like `class Foo { 1+1; };`. However, using an IIFE to initialize a field is allowed, as shown in the following example:

class Foo {
    foo: string = (function bar(){
        console.log("testing");
        return "value";
    }());
};

new Foo();

If you run the above code, you will see `testing` printed on the console.

It's also important to note that you cannot define a function inside a class like this:

class Foo {
    function bar(){
        console.log('testing');
    );
}

The correct way to define a method in a class is illustrated below:

class Foo {
    bar(){
        console.log('testing');
    );
}

Exploring Immediately Invoked Function Expressions in TypeScript

Answer №1

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