While it is technically correct to assign to parameters from within function bodies, it reduces code readability because developers won’t be able
to tell whether the original parameter or some temporary variable is being accessed without going through the whole function. Moreover, some
developers might also expect assignments of function parameters to be visible to callers, which is not the case, and this lack of visibility could
confuse them. Instead, all parameters, caught exceptions, and foreach parameters should be treated as constants.
Noncompliant Code Example
function MyClass(name, strings) {
name = foo; // Noncompliant
for (var str of strings) {
str = ""; // Noncompliant
}
}
Exceptions
There is a common pattern in JavaScript to overwrite certain parameters depending on other parameters that are optional. For example, a callback is
by convention always passed in the last position. If a parameter in a previous position was not passed, the callback will be passed in its position
instead.
Therefore, the rule ignores parameter reassignments that are inside an if statement block.
function f(param, optionalParam, cb) {
if (typeof optionalParam === 'function') {
cb = optionalParam;
optionalParam = {};
}
}
