JS代码的书写逻辑以及作用不是很清楚

Question

在尝试解析JS代码的逻辑，遇到下面这一段代码，不是很理解，希望能大致解释一下下面这段代码的作用。

function l(b, d, c, f) {
        if (b[j] === d && d[j] === b)
            return m;
        b[j] = d;
        d[j] = b;
        var k = function(a, c) {
            return null !== a && a !== e && a[c] !== e
        }, i;
        for (i in d)
            !k(b, i) && k(d, i) && c.push("expected has key " + i + '", but missing from actual.');
        for (i in b)
            !k(d, i) && k(b, i) && c.push('expected missing key "' + i + '", but present in actual.');
        for (i in d)
            i !== j && (a.equals(b[i], d[i], c, f) || f.push('"' + i + '" was "' + (d[i] ? d[i].toString() : d[i]) + '" in expected, but was "' + (b[i] ? b[i].toString() : b[i]) + '" in actual.'));
        a.isArray(b) && a.isArray(d) && b.length !== d.length && f.push("arrays were not the same length");
        delete b[j];
        delete d[j];
        return 0 === c.length && 0 === f.length
    }

Answer 1

第一，翔一样的代码我们为什么要去理解它？
第二
for(i in d)说明d可能是数组，那么b[j]===d是什么意思？那个j是怎么来的？然后b还是一个二维数组，同时b的第j+1的值还是d，这代码闹着玩呢？同理那个b也是一样