quick-lint-js

Find bugs in JavaScript programs.

E0075: indexing requires an expression

The syntax for indexing is expr1[expr2]. It is an error to omit the expression between [ and ]:

let colorToCode = {
  red:   '#ff0000',
  green: '#00ff00',
  blue:  '#0000ff',
};
let color = prompt();
document.body.style.color = colorToCode[];

let newFriends = friends[];
newFriends.push("Alice");
console.log(friends, "=>", newFriends);

To fix this error, write an expression between [ and ]:

let colorToCode = {
  red:   '#ff0000',
  green: '#00ff00',
  blue:  '#0000ff',
};
let color = prompt();
document.body.style.color = colorToCode[color];

Alternatively, to copy an array, create a new array and spread the old array into the new array:

let newFriends = [...friends];
newFriends.push("Alice");
console.log(friends, "=>", newFriends);

Documentation for other errors