What is the most efficient way to perform an inline property check and return a boolean value

Question

What is the most efficient way to perform an inline property check and return a boolean value

Can someone help me with optimizing my TypeScript code for a function I have?

function test(obj?: { someProperty: string}) {
  return obj && obj.someProperty;
}

Although WebStorm indicates that the return value should be a boolean, the TypeScript compiler is showing an error stating that it could be either undefined or string.

Here's my question:

What is the correct way to write an inline property check in TypeScript that always returns a boolean?

I thought about using double negation like this:

function test(obj?: { someProperty: string}) {
  return !!(obj && obj.someProperty);
}

But I understand that this may not be ideal for everyone.

javascript typescript webstorm

Answer 1

Answer №1

Here is a potential solution for you:

function checkProperty(obj?: { prop: string }) {
  return obj && obj.prop && true || false;
}

Answer 2

Here is a potential solution for you:

function checkProperty(obj?: { prop: string }) {
  return obj && obj.prop && true || false;
}

Answer 3

Answer №2

When using the && operator, there is no implicit casting into boolean. Instead, the following logic applies:

A && B && C
// If A is falsy, return A
// Else, return B && C
//      If B is falsy, return B
//      Else, return C

In your scenario, you have three potential outcomes:

If obj is undefined, it will return undefined.
If obj is defined but someProperty is undefined, it will also return undefined.
If obj and someProperty are both defined, it will return the value of some property (which in this case is a string).

Answer 4

When using the && operator, there is no implicit casting into boolean. Instead, the following logic applies:

A && B && C
// If A is falsy, return A
// Else, return B && C
//      If B is falsy, return B
//      Else, return C

In your scenario, you have three potential outcomes:

If obj is undefined, it will return undefined.
If obj is defined but someProperty is undefined, it will also return undefined.
If obj and someProperty are both defined, it will return the value of some property (which in this case is a string).

Answer 5

Answer №3

To transform your return value into a boolean, you can use the following code snippet:

function checkValue(obj?: { someProperty: string}) {
  return Boolean(obj && obj.someProperty);
}

Here is the JSFiddle link for reference: https://jsfiddle.net/oq4jr518/

Answer 6

To transform your return value into a boolean, you can use the following code snippet:

function checkValue(obj?: { someProperty: string}) {
  return Boolean(obj && obj.someProperty);
}

Here is the JSFiddle link for reference: https://jsfiddle.net/oq4jr518/

What is the most efficient way to perform an inline property check and return a boolean value

Answer №1

Answer №2

Answer №3

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