js 语法总结

js 是使用比较灵活的语言，语法 书写比较灵活，在js中function具有非常大的灵活性，function代码本身不仅允许被执行，还允许对值域范围内的代码进行扩展，支持在函数代码执行后再返回可继续执行的函数，同时可采用类似对象操作的方法对位函数增加属性或方法，参见示例：

function circularHeatChart() {
    var margin = {top: 20, right: 20, bottom: 20, left: 20},
    innerRadius = 50,
    numSegments = 24,
    segmentHeight = 20,
    domain = null,
    range = ["white", "red"],
    accessor = function(d) {return d;},
    radialLabels = segmentLabels = [];

    function chart(selection) {
        //==================在d3中选择器使用each进行选择器的遍历，对set、map对象使用forEach进行成员数据遍历===
        selection.each(function(data) {
            var svg = d3.select(this);

            var offset = innerRadius + Math.ceil(data.length / numSegments) * segmentHeight;
            g = svg.append("g")
                .classed("circular-heat", true)
                .attr("transform", "translate(" + parseInt(margin.left + offset) + "," + parseInt(margin.top + offset) + ")");

            var autoDomain = false;
            //=========返回数组中的最大值、最小值,使用accessor的目的是为了具有扩展性=====
            if (domain === null) {
                domain = d3.extent(data, accessor);
                autoDomain = true;
            }

            //====================可以用线性比例尺返回特定范围内的颜色值===========================
            var color = d3.scale.linear().domain(domain).range(range);
            if(autoDomain)
                domain = null;

            //=============这个图还不是很灵活，图形360度绘制的弧度数量=numSegment，当绘制的数据数量大于numSegment，逐层向外扩展绘制
            g.selectAll("path").data(data)
                .enter().append("path")
                .attr("d", d3.svg.arc().innerRadius(ir).outerRadius(or).startAngle(sa).endAngle(ea))
                .attr("fill", function(d) {return color(accessor(d));});


            // Unique id so that the text path defs are unique - is there a better way to do this?
            var id = d3.selectAll(".circular-heat")[0].length;

            //Radial labels
            var lsa = 0.01; //Label start angle
            var labels = svg.append("g")
                .classed("labels", true)
                .classed("radial", true)
                .attr("transform", "translate(" + parseInt(margin.left + offset) + "," + parseInt(margin.top + offset) + ")");

            labels.selectAll("def")
                .data(radialLabels).enter()
                .append("def")
                .append("path")
                .attr("id", function(d, i) {return "radial-label-path-"+id+"-"+i;})
                .attr("d", function(d, i) {
                    var r = innerRadius + ((i + 0.2) * segmentHeight);
                    return "m" + r * Math.sin(lsa) + " -" + r * Math.cos(lsa) + 
                            " a" + r + " " + r + " 0 1 1 -1 0";
                });

            labels.selectAll("text")
                .data(radialLabels).enter()
                .append("text")
                .append("textPath")
                .attr("xlink:href", function(d, i) {return "#radial-label-path-"+id+"-"+i;})
                .style("font-size", 0.6 * segmentHeight + 'px')
                .text(function(d) {return d;});

            //Segment labels
            var segmentLabelOffset = 2;
            var r = innerRadius + Math.ceil(data.length / numSegments) * segmentHeight + segmentLabelOffset;
            labels = svg.append("g")
                .classed("labels", true)
                .classed("segment", true)
                .attr("transform", "translate(" + parseInt(margin.left + offset) + "," + parseInt(margin.top + offset) + ")");

            labels.append("def")
                .append("path")
                .attr("id", "segment-label-path-"+id)
                .attr("d", "m0 -" + r + " a" + r + " " + r + " 0 1 1 -1 0");

            labels.selectAll("text")
                .data(segmentLabels).enter()
                .append("text")
                .append("textPath")
                .attr("xlink:href", "#segment-label-path-"+id)
                .attr("startOffset", function(d, i) {return i * 100 / numSegments + "%";})
                .text(function(d) {return d;});
        });

    }

    /* Arc functions */
    ir = function(d, i) {
        return innerRadius + Math.floor(i/numSegments) * segmentHeight;
    }
    or = function(d, i) {
        return innerRadius + segmentHeight + Math.floor(i/numSegments) * segmentHeight;
    }
    sa = function(d, i) {
        return (i * 2 * Math.PI) / numSegments;
    }
    ea = function(d, i) {
        return ((i + 1) * 2 * Math.PI) / numSegments;
    }

    /* Configuration getters/setters */
    chart.margin = function(_) {
        if (!arguments.length) return margin;
        margin = _;
        return chart;
    };

    chart.innerRadius = function(_) {
        if (!arguments.length) return innerRadius;
        innerRadius = _;
        return chart;
    };

    chart.numSegments = function(_) {
        if (!arguments.length) return numSegments;
        numSegments = _;
        return chart;
    };
 
    chart.accessor = function(_) {
        if (!arguments.length) return accessor;
        accessor = _;
        return chart;
    };

    return chart;
}

可使用变量赋值的方式调用函数circularHeatChart，调用完成后该变量既拥有了circularHeatChart的返回函数，可通过call等方式执行该变量，完成函数调用，示例代码：

var chart = circularHeatChart()
    .segmentHeight(20)
    .innerRadius(20)
    .numSegments(24)
    .radialLabels(["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"])
    .segmentLabels(["Midnight", "1am", "2am", "3am", "4am", "5am", "6am", "7am", "8am", "9am", "10am", "11am", "Midday", "1pm", "2pm", "3pm", "4pm", "5pm", "6pm", "7pm", "8pm", "9pm", "10pm", "11pm"])
    .margin({top: 20, right: 0, bottom: 20, left: 280});

d3.select('#energychart')
    .selectAll('svg')
    .data([energyData])
    .enter()
    .append('svg')
    .call(chart);

当然对函数对象chart的调用执行也可以采用这样的方式：

chart(d3.select('#energychart')
    .selectAll('svg')
    .data([energyData])
    .enter()
    .append('svg'))