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Allgemeine Snippets

Auf dieser Seite sind verschiedene JavaScript Snippets zu allgemeinen Themen.

Die Snippets stellen Beispiele dar. Passe diese gerne für deine Zwecke an.

Inhaltsverzeichnis

    Prüfen, ob Variable null oder undefined ist

    let myVar = null;

if (myVar === undefined || myVar === null) {
    console.log(`Variable is either undefined or null.`);
} else {
    console.log(`Variable is defined and not null.`);
}
    Variable is either undefined or null.

    Prüfen, ob Variable eine Funktion ist

    let myFunction = function() {
    console.log("Hello world");
};

if (typeof myFunction === "function") {
    console.log("Variable is of function type.");
} else {
    console.log("Variable is not of function type.");
}
    Variable is of function type.

    Queue-Struktur in JavaScript

    class Queue {

    constructor() {
        this.items = [];
    }

    enqueue(element) {
        this.items.push(element);
    }

    dequeue() {
        if (this.isEmpty()) {
            return "Underflow";
        }
        return this.items.shift();
    }

    front() {
        if (this.isEmpty()) {
            return "Queue is empty";
        }
        return this.items[0];
    }

    isEmpty() {
        return this.items.length === 0;
    }

    size() {
        return this.items.length;
    }

    print() {
        console.log(this.items);
    }

}

const queue = new Queue();

queue.enqueue(1);
queue.enqueue(2);
queue.enqueue(3);

console.log("Queue elements");
queue.print();

console.log("Front element:", queue.front());
console.log("Dequeued element:", queue.dequeue());
console.log("Queue size:", queue.size());
console.log("Is empty:", queue.isEmpty());
    Queue elements
[ 1, 2, 3 ]
Front element: 1
Dequeued element: 1
Queue size: 2
Is empty: false

    Prüfen, ob Variable eine Funktion ist

    let myFunction = function() {
    console.log("Hello world");
};

if (typeof myFunction === "function") {
    console.log("Variable is of function type.");
} else {
    console.log("Variable is not of function type.");
}
    Variable is of function type.

    Stack-Struktur in JavaScript

    class Stack {

    constructor() {
        this.items = [];
    }

    push(element) {
        this.items.push(element);
    }

    pop() {
        if (this.isEmpty()) {
            return "Underflow";
        }
        return this.items.pop();
    }

    peek() {
        return this.items[this.items.length - 1];
    }

    isEmpty() {
        return this.items.length === 0;
    }

    size() {
        return this.items.length;
    }

    print() {
        console.log(this.items);
    }
    
}

const stack = new Stack();

stack.push(1);
stack.push(2);
stack.push(3);

console.log("Stack elements");
stack.print();

console.log("Top element:", stack.peek());
console.log("Popped element:", stack.pop());
console.log("Stack size:", stack.size());
console.log("Is empty?", stack.isEmpty());
    Stack elements
[ 1, 2, 3 ]
Top element: 3
Popped element: 3
Stack size: 2
Is empty? false

    Zwei Variablen vertauschen

    let variableOne = "John";
let variableTwo = "Kate";

console.log("Before swapping");
console.log(`variableOne: ${variableOne}`);
console.log(`variableTwo: ${variableTwo}`);
console.log("=====");

// Swapping variables
let temp = variableOne;
variableOne = variableTwo;
variableTwo = temp;

console.log("After swapping");
console.log(`variableOne: ${variableOne}`);
console.log(`variableTwo: ${variableTwo}`);
    Before swapping
variableOne: John
variableTwo: Kate
=====
After swapping
variableOne: Kate
variableTwo: John

    Parameter in setTimeout übergeben

    function myFunction(parameter) {
    console.log("Parameter:", parameter);
}

let myParameter = "Hello world";
setTimeout(function() {
    myFunction(myParameter);
}, 1000);
    Parameter: Hello world

    Daten in Konsole eingeben

    const readline = require('readline').createInterface({
    input: process.stdin,
    output: process.stdout
})

readline.question('What is your name? ', name => {
    console.log(`Hello ${name}` )
    readline.close()
});
    What is your name? Max
Hello Max

    Umgebungsvariablen setzen

    Bei der Ausführung von JS-Dateien in NodeJS kann man Umgebungsvariablen in das Script hineingeben.

    const id = process.env.USER_ID
const key = process.env.USER_KEY

console.log(id)
console.log(key)
    Verwendung 
    USER_ID=1 USER_KEY=somekey node common_environment_variables.js
    1
somekey

    Fehler abfangen in try-catch

    Der try-catch Block funktioniert wie eine Art Auffangschale. Vor allem der catch Block. Dieser fängt alle, im try Block, geworfenen Fehler auf und kann sie entsprechend behandeln.

    const myArray = [10, 23, 29, 34, 7, 39, 40];

try {
    
    if (myVar < 10) {
        throw new Error("My var is false");
    }

} catch (error) {
    console.log("ERROR IN CATCH:", error);
} finally {
    console.log("Done");
}
    ERROR IN CATCH: ReferenceError: myVar is not defined

    Typ der Variable ermitteln

    Für die Ermittlung des Typs einer Variable, kann man sich eine Hilfs-Funktion schreiben.

    function getType(obj) {
    return Object.prototype.toString.call(obj).slice(8, -1);
}

console.log(getType(42));
console.log(getType("Hallo"));
console.log(getType(true));
console.log(getType([]));
console.log(getType({}));
console.log(getType(null));
console.log(getType(undefined));
console.log(getType(new Date()));
console.log(getType(/regex/));
console.log(getType(() => {}));
    Number
String
Boolean
Array
Object
Null
Undefined
Date
RegExp
Function