The successful conversion of Typescript to a number is no longer effective

Just the other day, I was successfully converting strings to numbers with no issues. However, today things have taken a turn for the worse. Even after committing my changes thinking all was well, I now find that when attempting to cast in different ways, I end up with NaN. It's as if something is affecting the variable where I store the casted values (because they appear fine when logged with console.log) – so what could I possibly be doing wrong?

Here's the code snippet:


totalPrice: number;
total: number;

if (this.cart_articles) {
    for (let article of this.cart_articles) {
        this.totalPrice += parseFloat(article.price);
        console.log(this.totalPrice); 
        console.log(parseFloat(article.price));
    }
    this.total = this.totalPrice + (this.totalPrice * 0.18);
    this.iva = this.totalPrice * 0.18;
}

Despite logging the values before assignment and seeing them being correctly casted, the variables total, totalPrice, and iva all end up as NaN. How can I go about resolving this issue? Apologies, but it's clear that I'm still quite new to all of this.

Answer №1

Ensure to set the initial value of totalPrice; otherwise, it will result in being undefined, and performing any arithmetic operation with undefined will yield NaN.

totalPrice= 0;
total = 0;

As a side note, you can optimize this using reduce:

if (this.cart_articles) {
    this.totalPrice = this.cart_articles.reduce((totalPrice, article) => totalPrice += parseFloat(article.price), 0);
    this.total = this.totalPrice + (this.totalPrice * 0.18);
    this.iva = this.totalPrice * 0.18;
}

Answer №2

Definition of numbers according to documentation: All numbers in TypeScript are considered as floating point values and are given the type number.

To convert strings to numbers, you can use the unary '+' operator. Additionally, if you try to parse a null value, it will result in NaN, but by casting it with the '+' operator, it will be converted to 0.

console.log(parseFloat(null)) // <-- NaN
console.log(+null) // <-- 0

Answer №3

One way to convert strings to numbers is by using Number()

let num1: string = '3.5';
let num2: string = '5.2'
var result: number;

result = Number(num1) + Number(num2);
console.log(result) // 8.7

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