I used logical assignments like b = a || [] in Javascript before, and there are many questions on SO about it.
To mention some:
- What does the construct x = x || y mean?
- JavaScript variable assignment with OR vs if check
- How does javascript logical assignment work?
And from what I read, b = a || [] is legit code.
However, I noticed in a recent case (checking for a variable set by another script), that this code does not work as I expected.
I assumed the code would check whether a is falsy, and if so [] would be assigned to b. Since undefined is falsy, I excepted the code to work and assign [] in the case when a was not defined.
But this code causes an error:
let b;
b = a || [];
console.log(b);
a = ["1", "2", "3"];
b = a || [];
console.log(b);
wheras
let b;
b = typeof a == "undefined" ? [] : b;
console.log(b);
a = ["1", "2", "3"];
b = a || [];
console.log(b);
does not.
And why is it causing an error, when the error says Uncaught ReferenceError: a is not defined, which implies a is undefined?
When can I use the logical assignment? Only when it is guaranteed that the variable (a) is at least declared?
