Using the union/intersection operators when accessing an index in array?

Question

I have a function that uses lodash's template method to dynamically create files and generate code within them.

Anyway, I encountered a bug that has me scratching my head. Googled around, couldn't find an answer.

Suppose I have the following array,

const myMap = [1, 2, 3, 4, 5, 6, 7];

What am I really accessing when I do the following?

console.log(myMap[1|4]); // 6
console.log(myMap[4|1]); // 6
console.log(myMap[4|1|4|1|1|1|1]); // 6
console.log(myMap[4|1|3|1|1|1|1]); // undefined

console.log(myMap[1&4]); // 1
console.log(myMap[1&5]); // 2
console.log(myMap[5&1]); // 2
console.log(myMap[1&6]); // 1

// combining the is also valid javascript, apparently:
console.log(myMap[5&1&5|2]); // 4

I feel like I'm missing something elementary, what's going on here?

Edit

Likewise, I can do this with objects:

const obj = { hello:'world' }
console.log(a['hello' & '']); // undefined
console.log(a['hello' | '']); // undefined
console.log(a['hello' || '']); // 'world' (obviously)

| is a bitwise "or". developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…. & is a bitwise "and" developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Marc
– Marc, Commented Dec 20, 2022 at 18:32

Brother58697 · Accepted Answer · 2022-12-20 18:32:48Z

1

JS is evaluating the expression inside the square brackets, so for myMap[1|4] it evaluates 1|4 where | is a bitwise OR, and 1|4 == 5 which is why you're getting 6 === myMap[5]

answered Dec 20, 2022 at 18:32

Brother58697

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