Why Do Event Listeners in a For Loop Target the Last Object?

addEventListener Using a For Loop and Passing Values

When using a for loop to add event listeners to multiple objects, the last object often becomes The target for all listener relocations. This article will solve this problem and provide a corrected code using closures:

Problem overview:

Trying to use a loop to add event listeners to multiple objects, But ultimately all listeners target the same object (the last one).

Correction code:

Closing is a way to prevent such problems. The modified code is as follows:

// 函数在点击时运行：
function makeItHappen(elem, elem2) {
    var el = document.getElementById(elem);
    el.style.backgroundColor = "red";
    var el2 = document.getElementById(elem2);
    el2.style.backgroundColor = "blue";
}

// 自动加载函数以添加侦听器：
var elem = document.getElementsByClassName("triggerClass");

for (var i = 0; i < elem.length; i += 2) {
    (function () {
        var k = i + 1;
        var boxa = elem[i].parentNode.id;
        var boxb = elem[k].parentNode.id;
        elem[i].addEventListener("click", function() { makeItHappen(boxa, boxb); }, false);
        elem[k].addEventListener("click", function() { makeItHappen(boxb, boxa); }, false);
    }()); // 立即调用
}

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