Overlapping Conditions in Typescript

Imagine having a straightforward piece of logic like this:

let bool = false

const seven = 7
const arr = [1,2,3,4,5,6,7]
    
arr.forEach(element => {
    if (element === seven) {
        bool = true
    }
});

Now the goal is to execute a function if "bool" is set to true:

if (bool === true){
    doSomething()
}

However, Typescript raises an error in this scenario:

This condition will always return 'false' since the types 'false' and 'true' have no overlap.

Despite knowing that logically bool will be true when the condition block is triggered, Typescript still gives an error. How can this issue be resolved?

Answer №1

Surprisingly, I recently discovered that the Typescript compiler would raise an issue with a seemingly innocuous condition statement like this:

if (bool === true)

Interestingly enough, it turns out that this syntax is equivalent to:

if (bool)

So in reality, you have a few options:

  1. Stick with the conventional way: if (bool) { ... } (the best choice)
  2. Explicitly declare the type as boolean:
    if((bool as boolean) === true ) { ... }
    (it may work, but it's not recommended)

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