If statement, is the shortened version readable enough?
The second part of the condition in the first method (someVar2[i].disabled = (someVar3.find("." + someVar4).length == 0)) is only an assignment and is always evaluated to true.

It is clearer to use only the first part of the condition as a condition in if (someVar1 !== "someString") and move assignment inside the if statement, similarly as you did in the second method. 

Regarding the second method, I would avoid using names such as bool as they are keywords. Use another name instead. 

Also, in this particular case you are assigning value to variable 'bool' and then use it only once. You could assign the value directly to someVar2[i].disabled.

if (someVar1 !== "someString") {
  someVar2[i].disabled = someVar3.find("." + someVar4).length == 0;
}


You could also use inline if:

someVar2[i].disabled = (someVar1 !== "someString") ? (someVar3.find("." + someVar4).length == 0) : &lt;defaultValue&gt;;