Javascript :: Checking == Or Just Mutating The Variable?

Imagine I had a variable called X.Let's say every 5 seconds I wanted to make X = true. (it could be either true or false in between these 5 seconds, but gets reset to true when the 5 seconds are up).

Would it be more efficient to check if the value is already true, then if not, reassign it to true? Or just have X = true?in other words, which would run faster?

if(x==false){
x = true;
}
vs
x = true;

On one hand, the first program won't mutate the variable if it doesn't have to. On the other hand, the second program doesn't need to check what X is equal to; it dives straight in.