JSHint shows the error: "Function declared within loop referencing an outer scope variable may lead to confusing semantics". How can I improve the following code to get rid of the warning?

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];
    }
};

JSHint shows the error: "Function declared within loop referencing an outer scope variable may lead to confusing semantics". How can I improve the following code to get rid of the warning?

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];
    }
};

• javascript
• loops
• closures
• jshint

• It would help us help you if you showed us an example of the structure of operators. Not least because Object(operators) looks quite odd looks quite odd... – T.J. Crowder Commented Jan 25, 2018 at 11:49
• This is operators. – Kasia Commented Jan 25, 2018 at 13:05
• this.operators = {"operators": { "^": 1, "*": 2, "/": 2, "%": 2, "+": 3, "-": 3, }, "functions": { "log": 0, "sin": 0, "cos": 0, "tan": 0, }, "brackets": { "open": ["("], "close": [")"] }, "equal": { "=": 4 } }; – Kasia Commented Jan 25, 2018 at 13:05
• To improve the question, use the "edit" link under the question, not ments (particularly not when you need code formatting). – T.J. Crowder Commented Jan 25, 2018 at 13:07
• @Kasia You might want to change your data structure into having a single level only, like {"^": {prec: 1, type: "op"}, "*": {prec: 2, type: "op"}, "log": {prec: 0, type:"fn"}, "(": {prec: 4, type:"open"} or so. (Although your structure for the brackets doesn't seem to fit in there anyway) – Bergi Commented Jan 25, 2018 at 13:27

2 Answers 2

You are supposed not to use the function expression inside the loop body, but instead declare it outside:

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];
    }
}

Of course the whole thing could be simplified by just using includes instead of some, and find instead of the loop:

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];
}

And finally, Object.keys(…).includes(…) can be simplified to operator in operators[key].

Add it before calling the function, this one will bypass that check

/* jshint -W083 */