为什么需要合并两个元件的属性？因为开发元件时，用户以json object形式传递参数进来，你准备开放10个参数，但是用户可能只传递了5个，你的代码如果去访问其余5个属性，就会出现notdefined错误，你不可能在内部一一去判断某个属性是否定义。为了省事，就定义一个预设的参数元件，然后和用户传入的参数元件合并。

比如：

//定义元件=======================
yjCurveDefaultOption = {
    rawData: null,
    renderTo: "",
    xAxisTitle: "",
    xAxisUnit: "",
    yAxisTitle: "",
    yAxisUnit: "",
    chartTitle: "",
    xAxisIsDatetime: false
}

yjCurve = function (option) {
    //合并用户给的参数和预设参数，如果不合并，后面可能访问到没有定义的属性报错
    option = $.extend({}, yjCurveDefaultOption, option);

    build();

    function build() {
    }
}

//使用元件========================
var rawData1 = [[2.5, 12907]];

var c1 = new yjCurve({
    xAxisIsDatetime: false,
    rawData: rawData1,
    xAxisTitle: "ShotCount",
    renderTo: "Div1",
    chartTitle: "Mold Temperature",
    yAxisTitle: "Temperature",
    yAxisUnit: "℃"
});

如何合并两个元件的属性， 这里有详细讨论：

http://stackoverflow.com/questions/171251/how-can-i-merge-properties-of-two-javascript-objects-dynamically

jquery本身有提供这样的函数：

// merge options object into settings object
var settings = { validate: false, limit: 5, name: "foo" };
var options  = { validate: true, name: "bar" };
jQuery.extend(settings, options);
// now the content of settings object is the following:
// { validate: true, limit: 5, name: "bar" }

var defaults = { validate: false, limit: 5, name: "foo" };
var options = { validate: true, name: "bar" };

/* merge defaults and options, without modifying defaults */
var settings = $.extend({}, defaults, options);
// the content of settings variable is now the following:
// {validate: true, limit: 5, name: "bar"}
// defaults and options variable remained the same

hightcharts.src.js里面的函数：

function merge() {
    var i,
	len = arguments.length,
	ret = {},
	doCopy = function (copy, original) {
		var value, key;

		for (key in original) {
		    if (original.hasOwnProperty(key)) {
		        value = original[key];

		        // An object is replacing a primitive
		        if (typeof copy !== 'object') {
		            copy = {};
		        }

		        // Copy the contents of objects, but not arrays or DOM nodes
		        if (value && typeof value === 'object' && Object.prototype.toString.call(value) !== '[object Array]'
						&& typeof value.nodeType !== 'number') {
		            copy[key] = doCopy(copy[key] || {}, value);

		            // Primitives and arrays are copied over directly
		        } else {
		            copy[key] = original[key];
		        }
		    }
		}
		return copy;
	};

    // For each argument, extend the return
    for (i = 0; i < len; i++) {
        ret = doCopy(ret, arguments[i]);
    }

    return ret;
}