The negation operator in Typescript is failing to negate as expected

When a user changes a multiselect element, there is a function that runs to control the visibility of an error message:

  getVisibility(multiselect) {
    if ((multiselect.selectedCategories.length < 1 && !multiselect.allSelected) && this.submitted) {
      return 'visible'
    } else {
      return 'hidden'
    }
  }

However, in this particular block of code:

if ((multiselect.selectedCategories.length < 1 && !multiselect.allSelected) && this.submitted)

The situation arises where multiselect.allSelected is false, but !multiselect.allSelected also evaluates to false.

Here are the images depicting the issue:

picture1

picture2

This leads to the question: Why does adding the not operator (!) not change the boolean value?

angulartypescriptoperatorsboolean-logic

Answer №1

Typescript not operator isn't functioning as expected

Even though Typescript is just enhanced JavaScript, sometimes the not operator may not work properly. This could be due to issues with Chrome Dev Tools and/or TypeScript source maps.

Here's what I do to troubleshoot:

  • Firstly, I execute the command in the console to double-check.
  • Next, I disable source maps, as they can sometimes cause discrepancies (Chrome Typescript debugging references wrong 'this')

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