• 实现jQuery选择器功能 $(‘.box1 .c1, .box2 #c2’)

    html&&css

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.box > div {
    width: 100px;
    height: 50px;
    border: 1px solid red;
    margin-top: 20px;
}
<div class="box1 box">
    <div class="c1"></div>
    <div class="c2"></div>
</div>
<hr>
<div class="box2 box">
    <div id="c1"></div>
    <div class="c2"></div>
</div>

JS

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//遍历器
var each = function (arr, callback) {
    for (var i = 0; i < arr.length; i++) {
        if (callback.call(arr[i], i, arr[i]) === false) {
            break;
        }
    }
};
//去首尾空格
var myTrim = function (str) {
    if (String.prototype.trim) {
        return str.trim();
    } else {
        return str.replace(/^\s+|\s+$/g, '')
    }
}
/*基础查询方法*/
var _get = function (selector, context, list) {
    list = list || [];
    context = context || document;
    var reg = /^(?:#([\w-]+)|\.([\w-]+)|(\w+)|(\*))$/,
        m = reg.exec(selector);
    if (m) {
        if (context.nodeType) {
            context = [context];
        }
        if (typeof context === 'string') {
            context = _get(context);
        }
        each(context, function () {
            if (m[1]) {
                list = _getId(m[1], this, list);
            } else if (m[2]) {
                list = _getClassName(m[2], this, list);
            } else if (m[3]) {
                list = _getTag(m[3], this, list);
            } else if (m[4]) {
                list = _getTag("*", this, list);
            }
        });
    }
    return list;
};
var _getId = function (Id, context, list) {
    list = list || [];
    list.push(document.getElementById(Id));
    return list;
};
var _getClassName = function (className, context, list) {
    list = list || [];
    if (document.getElementsByClassName) {
        list.push.apply(list, context.getElementsByClassName(className));
    } else {
        var tags = context.getElementsByTagName('*');
        for (var i = 0; i < tags.length; i++) {
            if ((' ' + tags[i] + ' ').indexOf(' ' + className + ' ') != -1) {
                list.push(tags[i]);
            }
        }
    }
    return list;
};
var _getTag = function (Tag, context, list) {
    list = list || [];
    list.push.apply(list, context.getElementsByTagName(Tag));
    return list;
};
/**************** 选择器的操作*********************/
var $ = function (selectors, context, list) {
    list = list || [];
    var selectNew = selectors.split(',');
    each(selectNew, function () {
        var tmp = this.split(' ');
        var c = context;
        for (var i = 0; i < tmp.length; i++) {
            if (!tmp[i])continue;
            c = _get(tmp[i], c);
        }
        list.push.apply(list, c);
    });
    return list;
};