CODEWITHSUNDEEP
javascripttypescriptlogical-operators
Madhur Maurya
Madhur Maurya

Reputation: 1070

Handle null >= 0 in Typescript

I have a simple check where I want to check if the given variable is >=0.

public print(value: any): void {
    if(value >= 0) {
      console.log('Greater than zero')
    }
  }

The catch here is when the incoming variable has value null, then it will become truthy and log the statement. Is there a clean way to avoid it, but not adding extra checks?

Upvotes: 4

Views: 7737

Answers (4)

Alex
Alex

Reputation: 1580

In JavaScript, I usually use the following:

`${value}` >= 0

// or

parseInt(value) >= 0

in TypeScript you can most likely use:

public print(value: any): void {
  if (+`${value}` >= 0) {
    console.log('Not less than zero')
  }
}

Upvotes: 0

VLAZ
VLAZ

Reputation: 28977

You can employ a type guard that will assure the compiler that you're not handling a null but a number. Moreover, it will make the code more correct, since with value: any this means you might get a boolean or a string passed in:

public print(value: any): void {
  if (typeof value === "number") {
    //value is definitely a number and not null
    if (value >= 0) {
      console.log('Greater than zero')
    }
  }
}

Playground Link

Now the code specifically verifies that you do get a number and then checks if it's more than or equal to zero. This means that a null or a non-number value would not be processed.

The type guard condition can be combined with the other for brevity:

public print(value: any): void {
  if (typeof value === "number" && value >= 0) {
    console.log('Greater than zero')
  }
}

Playground Link

Or extracted on its own to just reduce the nesting:

public print(value: any): void {
  if (typeof value !== "number")
    return;

  //value is definitely a number and not null
  if (value >= 0) {
    console.log('Greater than zero')
  }
}

Playground Link

Upvotes: 2

yeerk
yeerk

Reputation: 2677

If you codebase does not allow the use of null, just use undefined and use an implicit conversion, like so:

public print(value: any): void {
    if(value != undefined && value >= 0) {
        console.log('Greater than zero')
    }
}

This works because null == undefined (the double equals creates a type conversion, while the triple equals does not).

Upvotes: 1

Arnaud Claudel
Arnaud Claudel

Reputation: 3138

I don't see why you don't want to add a null-check.

An alternative is to use number instead of any but it will work only if your ts.conf enables strict null checks.

function print(value: number): void {
    if(value >= 0) {
      console.log('Greater than zero')
    }
}

print(null) // won't compile with strict null checks

Upvotes: 1

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