javascript - js函数在条件满足时不返回

Question

下面的代码，我找不到任何问题，但是，它有时会输出“'i' 不应高于 handlers.length”。

function callNext(req, res, handlers, cb) {
    let i = -1;
    let next = (thisObj) => {
        i += 1;

        if (i == handlers.length) {
            return cb();
        } else if (i > handlers.length) {
            console.log("'i' should not be higher than handlers.length.");
            console.log(handlers.length, i); // => 9 10
            return;
        }

        try {
            return handlers[i].call(thisObj || this, req, res, next);
        } catch (e) {
            this.onerror(e, req, res);
        }
    };

    return next();
}

因为根据人的逻辑，当i等于handlers.length时函数返回，下面的代码应该永远不会运行，这个问题真让我抓狂.

Answer 1

最简单的假设是某些处理程序错误地调用了 next 两次。

通常我会建议再次保护它，你可以使用类似的东西

function callNext(req, res, handlers, cb) {
   let lastCalledIndex;
   let next = (thisObj, index) => {
       if (index === lastCalledIndex) { 
           console.log("'next' called multiple times from handler");
           return; 
       }
       lastCalledIndex = index;
       if (i === handlers.length) {
           return cb();
       } else if (index > handlers.length) {
           console.log("'index' should not be higher than handlers.length.");
           console.log(handlers.length, index); // => 9 10
           return;
       }

       try {
           return handlers[index].call(thisObj || this, req, res, next.bind(undefined, thisObj, index + 1));
       } catch (e) {
           this.onerror(e, req, res);
       }
    };

    return next(this, 0);
}