How can I easily set the variable to false with the default value true?

Question

I usually set the properties of an object so that

// Boolean this.listening = config.listening || true; 

But config.listening is either true or false, in which case this.listening will always be true, because if config.listening false, it will be true.

Is there a better way to set these boolean properties without having to execute an if statement?

Is there an ifset function in javascript to test it, and not that it is equal?

Answer 1

You can use the ternary (conditional) operator as follows:

 this.listening = config.listening === false ? false : true; 

If config.listening is false , this.listening set to false . If this is a different value, it is set to true .

If you want to check if this is defined, you can use:

 this.listening = typeof config.listening !== "undefined" 

Literature:

• https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/Conditional_Operator

Answer 2

You need to check to make sure that it is not undefined, and not that it is a “false” value.

 this.listening = config.listening!==undefined ? config.listening : true; 

Answer 3

The fastest way is this.

 d = true; 

d returns true.

Then just use it! operator to switch the boolean from true to false.

 d = !d; 

d returns false.

Then again and again.

 d = !d; 

d returns true.