I am puzzled by the code:
$("#submit").prop("disabled", !canSubmit());

what does an exclamation mark mean

Question

The canSubmit function is declared earlier in the code. And then later we're setting the property too an element with the id "submit" as disabled. And then this !functhion() is added. What does that do?
Thank you.

Matt F. · Accepted Answer

Hi Nina,
``` javascript
$("#submit").prop("disabled", !canSubmit());
```
This code finds the element with the id of submit and assigns a property 'disabled' to it, with a value of true or false, depending on what is returned by canSubmit.
If canSubmit() returns a truthy value ("string", true, 1, 2, 3, etc.), the exclamation mark - which is the NOT operator in JavaScript  (also referred to as a 'bang') - will explicitly coerce that return value to to the boolean false. This would mean that the element with an id of submit would have a prop disabled='false
Similarly, if canSubmit returns a falsy value (false, 0, null, undefined) it will explicitly coerce the value to the boolean true. Meaning that the element with an id of submit would have a prop disabled='true'.
When you see the single bang, it means that a truthy value will become the boolean false, while falsy values will become the boolean true.
Here is a page on the NOT operator in JavaScript: https://msdn.microsoft.com/en-us/library/zz722703(v=vs.94).aspx

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Nina Kozlova

Nina Kozlova

I am puzzled by the code: $("#submit").prop("disabled", !canSubmit()); what does an exclamation mark mean

1 Answer

Matt F.

Matt F.

Nina Kozlova

Nina Kozlova