No Cond Assign

Disallows the use of the assignment operator, =, in conditional statements.

Use of the assignment operator within a conditional statement is often the result of mistyping the equality operator, ==. If an assignment within a conditional statement is required then this rule allows it by wrapping the assignment in parentheses.

Invalid:

let x;
if (x = 0) {
  let b = 1;
}

function setHeight(someNode) {
  do {
    someNode.height = "100px";
  } while (someNode = someNode.parentNode);
}

Valid:

let x;
if (x === 0) {
  let b = 1;
}

function setHeight(someNode) {
  do {
    someNode.height = "100px";
  } while ((someNode = someNode.parentNode));
}