Disallow Unreachable Code (no-unreachable)

A number of statements unconditionally exit a block of code. Any statements after that will not be executed and may be an error. The presence of unreachable code is usually a sign of a coding error.

function fn() {
    x = 1;
    return x;
    x = 3; // this will never execute
}

Rule Details

This rule is aimed at detecting unreachable code. It produces an error when a statements in a block exist after a return, throw, break, or continue statement. The rule checks inside the program root, block statements, and switch cases.

The following are considered warnings:

function foo() {
    return true;
    console.log("done");
}

function bar() {
    throws new Error("Oops!");
    console.log("done");
}

while(value) {
    break;
    console.log("done");
}

throw new Error("Oops!");
console.log("done");

The following patterns are not considered warnings (due to JavaScript function and variable hoisting):

function foo() {
    return bar();
    function bar() {
        return 1;
    }
}

function bar() {
    return x;
    var x;
}

switch (foo) {
    case 1:
        break;
        var x;
}

Version

This rule was introduced in ESLint 0.0.6.

Resources