JSHint 警告“在引用外部作用域变量的循环内声明的函数可能会导致语义混淆”。如何改进代码？

Question

JSHint 显示错误：“在引用外部作用域变量的循环内声明的函数可能会导致语义混淆”。如何改进以下代码以消除警告？

var getPrecedence  = function getPrecedence(operator, operators) {
    var keys = Object.keys(Object(operators));
    for (var i = 0, len = keys.length; i < len; i++) {
        var check = Object.keys(operators[keys[i]]).some(function (item) {
            return item === operator;
    });
    if (check) return operators[keys[i]][operator];
    }
};

Answer 1

你不应该在循环体内部使用函数表达式，而是在外部声明它：

function getPrecedence(operator, operators) {
    function isOperator(item) {
//  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
        return item === operator;
    }
    var keys = Object.keys(Object(operators));
    for (var i = 0, len = keys.length; i < len; i++) {
        var check = Object.keys(operators[keys[i]]).some(isOperator);
//                                                       ^^^^^^^^^^
        if (check) return operators[keys[i]][operator];
    }
}

当然，整个过程可以通过使用includes而不是some，而find不是循环来简化：

function getPrecedence(operator, operators) {
    var keys = Object.keys(Object(operators));
    var opkey = keys.find(key =>
        Object.keys(operators[key]).includes(operator)
    );
    if (opkey) return operators[opkey][operator];
}

最后，Object.keys(…).includes(…)可以简化为.operator in operators[key]