Every time I attempt to verify a string value in Typescript, this condition will consistently evaluate to true

I'm working with a variable called phone, which is a number type. My task is to verify that the first two digits of this phone number are not 33 or 32. In order to do this, I converted the number to a string and extracted the first and second digits for comparison.

  
let phoneText = this.phone.toString();
let digit1 = phoneText.charAt(0);
let digit2 = phoneText.charAt(1);
let twoDigits: string = digit1 + digit2;
if ((twoDigits != "33") || (twoDigits != "32")) {
    alert("Invalid");
}

However, I encountered an issue with the if statement and received an error message that I'm having trouble understanding.

This condition will always return 'true' since the types "33" and "32" have no overlap.ts(2367)
let start: "33"

Answer №1

When the number is 32: The first condition evaluates to true. Result: true.

When the number is 0 or any other number: The first condition evaluates to true. Result: true.

When the number is 33: The first condition evaluates to false. The second condition evaluates to true. Result: true.

This situation triggers the error. Only in this specific scenario will the second condition be considered. This leads to a comparison between 33 and 32, resulting in the no overlap error from TypeScript.

It can be likened to this example

let x = true;
if(Math.random() > 0.5 || x == false){
  console.log("hi");
}

The desired outcome should be:

let phoneText = this.phone.toString();
let digit1 = phoneText.charAt(0);
let digit2 = phoneText.charAt(1);
let twoDigits: string = digit1 + digit2;
if ((twoDigits != "33") && (twoDigits != "32")) {
    alert("Invalid");
}

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