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window.onload = function() {
    var check = document.getElementById("checkBox");
    var fru = document.getElementsByName("fruits");
    
    // ???????????
    check.onclick = function() {
        for (var i in fru) {
            fru[i].checked = check.checked;
        }
    };
    
    // ???????????
    for (var j = 0; j < fru.length; j++) {
        fru[j].onclick = function() {
            var fruitsCount = 0;
            for (var j = 0; j < fru.length; j++) {
                if (fru[j].checked === true) {
                    fruitsCount++;
                }
            }
            check.checked = (fru.length === fruitsCount);
        };
    }
}

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// ????????
var check = document.getElementById("checkBox");
// ????fruit checkbox????
var fru = document.getElementsByName("fruits");
// ??????????
check.onclick = function() {
    // ???fruit checkbox?checked??????????checked??
    for (var i in fru) {
        fru[i].checked = check.checked;
    }
};
// ????fruit checkbox?????
for (var j = 0; j < fru.length; j++) {
    fru[j].onclick = function() {
        // ???????fruit checkbox??
        var fruitsCount = 0;
        for (var j = 0; j < fru.length; j++) {
            if (fru[j].checked === true) {
                fruitsCount++;
            }
        }
        // ????fruit checkbox?????????????????
        check.checked = (fru.length === fruitsCount);
    };
}

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