function add(a:number, b:number):number {
return a+b;
}
let mynumber:any = "50";
let result:number = add(mynumber, 5);
console.log(result);
Why does the console print "505" without throwing an error in the "add" function?
If I had declared mynumber as : number, I would have received an error at the declaration line. Shouldn't I have gotten an error in this case too?
When you use type assertion, you are telling the compiler to treat mynumber as any. This special inbuilt type is compatible with any other type.
During runtime, if your add function receives a string instead of a number, it converts and concatenates the values. It's fortunate that this mismatch didn't cause a runtime error.
To better conceptualize types, consider them as sets, categories, or groups. For instance, when you define a variable as a number:
let x: number;
The variable x can encompass all the values within the numbers set, which has an infinite range of potential values.
There are various other infinite categories or groups (types) like the string type. Conversely, there are categories with a finite number of possible values, such as the boolean category.
You also have the option to declare a variable as a combination of multiple categories:
let x: number | boolean;
This line introduces a new group that can include an infinite array of potential values, including true, false, and all numbers.
When viewing types as sets, categories, or groups, it becomes clear why errors may not arise, for example in this scenario:
let myvalue: any = "50";
The myvalue is recognized as valid number because the any type encompasses all other types. Therefore, any can be interpreted as a valid number, boolean, string, etc.
One reason for this behavior is that the variable mynumber is declared as type any.
When you specify a variable as any, it essentially tells the type checker to ignore typing rules.
However, if you change the type to string, an error will occur:
let mynumber: string = "50";
let result:number = add(mynumber, 5); // error: Argument of type 'string' is not assignable to parameter of type 'number'
On the other hand, here are some examples where using any does not result in errors:
let a = "string" as any;
let b = /a+/g as any;
let c: number = a + b;
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