Weirdness in JS

While writing an SQL parser, noticed some weirdness when setting fields in an object with boolean/null keys. They can be accessed using a[true] or a.true or a['true']. This is because the key is converted to a string(when we access).

const a = {
    true: '1',
    false: '0',
    null: 'null'
}
console.log(a[true], a.true, a['true']) // 1
console.log(a[false], a.false, a['false']) // 0
console.log(a[null], a.null, a['null']) // null

This also has the same behavior when the key is computed.

const a = {
    [true]: '1',
    [false]: '0',
    [null]: 'null'
}
console.log(a[true], a.true, a['true']) // 1
console.log(a[false], a.false, a['false']) // 0
console.log(a[null], a.null, a['null']) // null

This is same as the first one -

const a = {
    ['true']: '1',
    ['false']: '0',
    ['null']: 'null'
}
console.log(a[true], a.true, a['true']) // 1
console.log(a[false], a.false, a['false']) // 0
console.log(a[null], a.null, a['null']) // null

So before accessing a field, ideally the type should be checked for string, unless its intended.

if(typeof key === 'string') {
    console.log(a[key])
} else {
    console.log(a[key.toString()])
}

This is not really in issue in typescript as it throws an error when the key is not a string or symbol. Unless any is used.