A dead store happens when a local variable is assigned a value that is not read by any subsequent instruction. Calculating or retrieving a value only to then overwrite it or throw it away, could indicate a serious error in the code. Even if it's not an error, it is at best a waste of resources. Therefore all calculated values should be used.
i = a + b; // Noncompliant; calculation result not used before value is overwritten i = compute();
i = a + b; i += compute();
This rule ignores initializations to -1, 0, 1, null, undefined, true, false, "",
[] and {}.
This rule also ignores variables declared with object destructuring using rest syntax (used to exclude some properties from object):
let {a, b, ...rest} = obj; // 'a' and 'b' are ok
doSomething(rest);
let [x1, x2, x3] = arr; // but 'x1' is noncompliant, as omitting syntax can be used: "let [, x2, x3] = arr;"
doSomething(x2, x3);