为什么jslint说我的变量超出范围？

Question

Why does jslint say that id_interval is out of scope? JavaScript is function scoped last time I checked.

Pub.elementLoaded = function (id, callback) {
    var isLoaded = document.getElementById(id);
    var id_interval = setInterval( function() {
        if (isLoaded) {
            callback();
            clearInterval(id_interval);
        }
    }, 1);
};

Answer 1

JSLint enforces what its author considers best practices, not the actual JavaScript syntactic rules. Quoting from jslint.com about variable declarations:

JSLint uses the intersection of the var rules and the let rules, and by doing so avoids the errors related to either. A name should be declared only once in a function. It should be declared before it is used.

In your code, id_interval is used inside its own declaration, at which point it strictly isn't declared yet.

Answer 2

A late answer for others like me who arrive here with the same question: as @GertG explains, JSLint just wants you to declare the variable before the block in which you use it.

You have to add var id_interval; before you use the setInterval() , and then remove var on the following line, because now you've already declared it:

Pub.elementLoaded = function (id, callback) {
    var isLoaded = document.getElementById(id);
    var id_interval;
    id_interval = setInterval( function() {
        if (isLoaded) {
            callback();
            clearInterval(id_interval);
        }
    }, 1);
};