Javascript 未捕获类型错误：无法读取属性'；getSelection'；空的

我使用下面的代码来模拟元素上的鼠标单击事件

var composeEl = $('.asf.T-I-J3.J-J5-Ji:visible')[0];

if (composeEl) {
    //Trigger mouse down event
    var mouseDown = document.createEvent('MouseEvents');
    mouseDown.initEvent('mousedown', true, false);
    composeEl.dispatchEvent(mouseDown)

    //Trigger mouse up event
    var mouseUp = document.createEvent('MouseEvents');
    mouseUp.initEvent('mouseup', true, false);
    composeEl.dispatchEvent(mouseUp)
}

它可以正常工作，但会在控制台中抛出此错误

Uncaught TypeError: Cannot read property 'getSelection' of null.

这个javascript代码有什么问题

Chrome在

content.js

文件中显示错误。我不包括这个文件。 这行有错误

var c=b.view.getSelection（）在下面的代码中

var m;if (!window.a) {
var t = function() {
    var b = window.self === window.top;
    this.k = (this.G = b) ? 0 : null;
    this.s = this.d = !1;
    this.j = this.i = -1;
    this.F = 1;
    this.c = {};
    this.q = [];
    var c = chrome.extension.connect({
        name: b ? "top" : "sub"
    });
    this.a = c;
    this.r = c.a || Math.ceil(975 * Math.random());
    c.onMessage.addListener(this.onMessage.bind(this));
    c.onDisconnect.addListener(this.v.bind(this));
    this.b(window, "scroll", this.O, !0);
    this.b(window, "keydown", this.u, !0);
    this.b(window, "keyup", this.u, !0);
    this.b(window, "mousedown", this.L, !0);
    this.b(window, "mouseup",
        this.M, !0);
    this.b(window, "blur", this.K, !0);
    this.b(document, "beforeload", this.I, !0);
    this.b(document, "DOMContentLoaded", this.J);
    b && this.b(window, "resize", this.N)
};
window.a = !0;
var x = {
        16: !0,
        17: !0,
        18: !0,
        45: !0,
        46: !0
    },
    C = ["VIDEO", "AUDIO", "OBJECT", "EMBED"],
    D = new RegExp(atob("eXRwbGF5ZXJcLmNvbmZpZ1xzKj1ccypcew=="));
m = t.prototype;
m.A = function(b, c, e, f) {
    try {
        var d = document.activeElement,
            n = d && 0 <= C.indexOf(d.tagName) ? d : null;
        n || (n = (d = document.elementFromPoint(this.i, this.j)) && 0 <= C.indexOf(d.tagName) ? d : null);
        for (var k =
                0, p, q, r, h, l = 0; l < C.length; l++) {
            for (var g = document.getElementsByTagName(C[l]), w = 0; w < g.length; w++)
                if (d = g[w], 3 != l || "application/x-shockwave-flash" == d.type.toLowerCase()) {
                    var s = d.src || d.data;
                    if (s && (s == b || s == c)) {
                        p = d;
                        break
                    }
                    if (!n && !q)
                        if (!s || s != e && s != f) {
                            var u = d.clientWidth,
                                v = d.clientHeight;
                            if (u && v) {
                                var y = d.getBoundingClientRect();
                                if (!(0 >= y.right + window.scrollX || 0 >= y.bottom + window.scrollY)) {
                                    var z = window.getComputedStyle(d);
                                    if (!z || "hidden" != z.visibility) {
                                        var A = u * v;
                                        A > k && 1.35 * u > v && u < 3 * v && (k = A, r = d);
                                        h || (h = d)
                                    }
                                }
                            }
                        } else q =
                            d
                }
            if (p) break
        }
        b = p || n || q || r || h;
        if (!b) return null;
        if ("EMBED" == b.tagName && !b.clientWidth && !b.clientHeight) {
            var B = b.parentElement;
            "OBJECT" == B.tagName && (b = B)
        }
        return this.g(b)
    } catch (E) {}
};
m.w = function(b, c, e) {
    try {
        for (var f = [], d, f = Array.prototype.concat.apply(f, document.getElementsByTagName("FRAME")), f = Array.prototype.concat.apply(f, document.getElementsByTagName("IFRAME")), n = 0; n < f.length; n++) {
            var k = f[n];
            if (parseInt(k.getAttribute("__idm_frm__")) == b) {
                d = k;
                break
            }
            if (!d) {
                var p = k.src;
                !p || p != c && p != e || (d = k)
            }
        }
        return this.g(d)
    } catch (q) {}
};
m.p = function() {
    var b = window.devicePixelRatio,
        c = document.width,
        e = document.body.scrollWidth;
    c && e && (b = c == e ? 0 : c / e);
    return b
};
m.n = function(b) {
    try {
        var c = b.getBoundingClientRect(),
            e = Math.round(c.width),
            f = Math.round(c.height);
        if (15 > e || 15 > f) return null;
        var d = document.documentElement,
            n = d.scrollHeight || d.clientHeight,
            k = Math.round(c.left) + b.clientLeft,
            p = Math.round(c.top) + b.clientTop;
        return k >= (d.scrollWidth || d.clientWidth) || p >= n ? null : {
            left: k,
            top: p,
            right: k + e,
            bottom: p + f,
            zoom: this.p()
        }
    } catch (q) {}
};
m.o = function() {
    this.a.postMessage([21,
        window.location.href
    ])
};
m.f = function(b) {
    if (b) {
        if (!this.H) {
            this.H = !0;
            this.b(window, "message", this.P);
            var c = document.createElement("script");
            c.src = chrome.extension.getURL("document.js");
            c.onload = function() {
                c.parentNode.removeChild(c)
            };
            document.documentElement.appendChild(c)
        }
        window.setTimeout(function() {
            window.postMessage([1], "/")
        }, 3E3)
    } else if ("loading" == document.readyState) this.t = !0;
    else {
        this.t = !1;
        b = document.getElementsByTagName("SCRIPT");
        for (var e = 0; e < b.length; e++)
            if (c = b[e], !c.src && D.test(c.innerText)) {
                b =
                    this.h();
                this.a.postMessage([34, b, -1, c.outerHTML]);
                break
            }
    }
};
m.P = function(b) {
    var c = b.data;
    c instanceof Array && b.origin == (document.origin || location.origin) && 2 == c[0] && this.a.postMessage([34, c[1], -1, c[2]])
};
m.D = function(b) {
    var c = b[2] || this.w(b[3], b[4], b[5]),
        e = c && this.c[c],
        e = e && this.n(e);
    this.a.postMessage([22, b[1], b[3], c, e])
};
m.C = function(b) {
    var c = !b[2],
        e = b[2] || this.A(b[3], b[4], b[5], b[6]);
    b = [23, b[1], e, !1];
    var f = e && this.c[e];
    if (f) {
        var d = this.n(f);
        d && (b[4] = d);
        c ? (b[5] = f.tagName, b[6] = f.src || f.data, b[7] = this.h()) :
            d || document.contains(f) || (b[3] = !0, delete this.c[e])
    }
    this.a.postMessage(b)
};
m.g = function(b) {
    try {
        var c = parseInt(b.getAttribute("__idm_id__"));
        c || (c = this.r << 10 | this.F++, b.setAttribute("__idm_id__", c));
        this.c[c] = b;
        return c
    } catch (e) {}
};
m.h = function(b) {
    var c;
    try {
        c = window.top.document.title
    } catch (e) {}
    if (c)
        if (c = c.replace(/[ \t\r\n\u25B6]+/g, " ").trim(), b) this.a.postMessage([24, b, c]);
        else return c
};
m.e = function(b) {
    if (!this.l) {
        var c = "\\b\\w+://(?:[%T]*(?::[%T]*)?@)?[%H.]+\\.[%H]+(?::\\d+)?(?:/(?:(?: +(?!\\w+:))?[%T/~;])*)?(?:\\?[%Q]*)?(?:#[%T]*)?".replace(/%\w/g,
            function(b) {
                return this[b]
            }.bind({
                "%H": "\\w\\-\u00a0-\ufeff",
                "%T": "\\w\\-.+*()$!,%\u00a0-\ufeff",
                "%Q": "^\\s\\[\\]{}()"
            }));
        this.l = new RegExp(c, "gi")
    }
    for (var e = []; c = this.l.exec(b);) e.push(c.shift());
    return e
};
m.m = function(b, c, e) {
    var f = [],
        d = {},
        n = "",
        k = "",
        p = !e,
        q;
    if (e && (q = b.getSelection(), !q || q.isCollapsed)) return f;
    var r = b.getElementsByTagName("A");
    if (r)
        for (var h = 0; h < r.length; h++) {
            var l = r[h];
            if (l && (p || q.containsNode(l, !0))) {
                var g = l.href;
                g && !d[g] && c.test(g) && (d[g] = f.push([g, 2, l.innerText || l.title]));
                e &&
                    d[g] && (n += l.innerText, n += "\n")
            }
        }
    if (r = b.getElementsByTagName("AREA"))
        for (h = 0; h < r.length; h++)(l = r[h]) && (p || q.containsNode(l, !0)) && (g = l.href) && !d[g] && c.test(g) && (d[g] = f.push([g, 2, l.alt]));
    if (r = p && b.getElementsByTagName("IFRAME"))
        for (h = 0; h < r.length; h++)(l = r[h]) && (p || q.containsNode(l, !0)) && (g = l.src) && !d[g] && c.test(g) && (d[g] = f.push([g, 4]));
    if (h = e && q.toString())
        for (l = this.e(h), n = this.e(n), h = 0; h < l.length; h++)(g = l[h]) && !d[g] && c.test(g) && 0 > n.indexOf(g) && (d[g] = f.push([g, 1]));
    if (n = (p || !f.length) && b.getElementsByTagName("IMG"))
        for (h =
            0; h < n.length; h++)(l = n[h]) && (p || q.containsNode(l, !0)) && ((g = l.src) && !d[g] && c.test(g) && (d[g] = f.push([g, 3, "<<<=IDMTRANSMITIMGPREFIX=>>>" + l.alt])), p && l.onclick && (k += l.onclick, k += "\n"));
    if (b = p && b.getElementsByTagName("SCRIPT")) {
        for (h = 0; h < b.length; h++) k += b[h].innerText, k += "\n";
        for (k = this.e(k); k.length;)(g = k.shift()) && !d[g] && c.test(g) && (d[g] = f.push([g, 5]))
    }
    return f
};
m.B = function(b, c) {
    for (var e = this.m(document, b, c), f = document.getElementsByTagName("IFRAME"), d = Array.prototype.push, n = 0; n < f.length; n++) try {
        var k =
            f[n],
            p = k.contentDocument;
        p && !k.src && d.apply(e, this.m(p, b, c))
    } catch (q) {}
    return e
};
m.u = function(b) {
    x[b.keyCode] && this.a.postMessage([31, b.keyCode, "keydown" == b.type])
};
m.L = function(b) {
    this.s && this.a.postMessage([28]);
    if (0 == b.button) {
        var c = b.view.getSelection();
        this.d = c && c.isCollapsed;
        this.a.postMessage([32, b.button, !0])
    }
};
m.M = function(b) {
    if (0 == b.button && (this.i = b.clientX, this.j = b.clientY, this.a.postMessage([32, b.button, !1]), this.d)) {
        this.d = !1;
        var c = b.view.getSelection();
        c && !c.isCollapsed && this.a.postMessage([26,
            b.clientX, b.clientY, this.p()
        ])
    }
};
m.K = function() {
    this.d = !1;
    this.a.postMessage([33])
};
m.O = function() {
    this.a.postMessage([29])
};
m.N = function(b) {
    b = b.target;
    this.a.postMessage([30, b.innerWidth, b.innerHeight])
};
m.I = function(b) {
    var c = b.target,
        e = c.tagName;
    0 <= C.indexOf(e) && b.url && (c = this.g(c), this.a.postMessage([25, c, e, b.url]))
};
m.J = function() {
    this.t && this.f()
};
m.onMessage = function(b) {
    switch (b[0]) {
        case 11:
            var c = b[2];
            if (c) {
                this.k = c;
                try {
                    window.frameElement && window.frameElement.setAttribute("__idm_frm__", c)
                } catch (e) {}
            }
            b[3] &&
                this.o();
            b[4] && this.f();
            break;
        case 17:
            b[1] && this.o();
            b[2] && this.f(!0);
            break;
        case 12:
            var c = this.B(b[4] ? new RegExp(b[4], "i") : null, b[2]),
                f = [27, b[1], this.k, c.length];
            b[3] || (f[4] = c, f[5] = window.location.href, this.G && (f[6] = window.location.href, f[7] = document.title));
            this.a.postMessage(f);
            break;
        case 13:
            this.s = b[1];
            break;
        case 14:
            this.h(b[1]);
            break;
        case 15:
            this.C(b);
            break;
        case 16:
            this.D(b)
    }
};
m.b = function(b) {
    var c = Array.prototype.slice.call(arguments);
    c[2] = c[2].bind(this);
    this.q.push(c);
    b.addEventListener.apply(b,
        c.slice(1))
};
m.v = function() {
    for (var b; b = this.q.shift();) {
        var c = b.shift();
        c.removeEventListener.apply(c, b)
    }
    this.a = this.r = null;
    window.a = !1
};
new t
};

var-m；如果（！window.a）{
var t=函数（）{
var b=window.self==window.top；
this.k=（this.G=b）？0:null；
this.s=this.d=！1；
这个.j=这个.i=-1；
这个。F=1；
这个.c={}；
这个.q=[]；
var c=chrome.extension.connect({
名称：b？“顶部”：“次级”
});
这个a=c；
this.r=c.a | | Math.ceil（975*Math.random（））；
c、 onMessage.addListener（this.onMessage.bind（this））；
c、 onDisconnect.addListener（this.v.bind（this））；
this.b（窗口，“滚动”，this.O，！0）；
this.b（窗口，“keydown”，this.u，！0）；
this.b（窗口，“keyup”，this.u，！0）；
this.b（窗口“mousedown”，this.L，！0）；
此.b（窗口，“鼠标悬停”，
这个。M，！0）；
this.b（窗口，“模糊”，this.K，！0）；
this.b（文档“beforeload”，this.I，！0）；
this.b（文件“DOMContentLoaded”，this.J）；
b&&this.b（窗口，“调整大小”，this.N）
};
window.a=！0；
变量x={
16: !0,
17: !0,
18: !0,
45: !0,
46: !0
},
C=[“视频”、“音频”、“对象”、“嵌入”]，
D=新的RegExp（atob（“eXRwbGF5ZXJcLmNvbmZpZ1xzKj1ccypcew=”）；
m=t.原型；
m、 A=函数（b，c，e，f）{
试一试{
var d=document.activeElement，
n=d&&0=y.bottom+window.scrollY）{
var z=window.getComputedStyle（d）；
如果（！z | |“隐藏”！=z.visibility）{
var A=u*v；
A>k&1.35*u>v&u<3*v&d（k=A，r=d）；
h | |（h=d）
}
}
}
}其他问题=
D
}
如果（p）中断
}
b=p | n | q | r | h；
如果（！b）返回null；
如果（“嵌入”==b.tagName&&！b.clientWidth&&！b.clientHeight）{
var B=B.parentElement；
“对象”==B.tagName&&（B=B）
}
返回此.g（b）
}捕获（E）{}
};
m、 w=功能（b、c、e）{
试一试{
对于（var f=[]，d，f=Array.prototype.concat.apply（f，document.getElementsByTagName（“FRAME”）），f=Array.prototype.concat.apply（f，document.getElementsByTagName（“IFRAME”）），n=0；ne | | 15>f）返回null；
var d=document.documentElement，
n=d.卷轴高度| | d.卷轴高度，
k=数学四舍五入（c.左）+b.客户端左，
p=数学圆（c.top）+b.clientTop；
返回k>=（d.scrollWidth | | d.clientWidth）| | p>=n？空：{
左:k,，
上图：p，
右:k+e,，
底部：p+f，
zoom:this.p（）
}
}捕获（q）{}
};
m、 o=函数（）{
这个.a.postMessage（[21，
window.location.href
])
};
m、 f=功能（b）{
如果（b）{
如果（！this.H）{
this.H=！0；
this.b（窗口，“消息”，this.P）；
var c=document.createElement（“脚本”）；
c、 src=chrome.extension.getURL（“document.js”）；
c、 onload=函数（）{
c、 parentNode.removeChild（c）
};
document.documentElement.appendChild（c）
}
setTimeout（函数（）{
window.postMessage（[1]，“/”）
}，3E3）
}否则如果（“加载”==document.readyState）this.t=！0；
否则{
this.t=！1；
b=document.getElementsByTagName（“脚本”）；
对于（var e=0；e