d3.select("#element") not working when code above the html element

This works:

<div id="chart"></div>
<script>var svg = d3.select("#chart").append("svg:svg");</script>

This doesn't:

<script>var svg = d3.select("#chart").append("svg:svg");</script>
<div id="chart"></div>

I tried wrapping the code in a jquery document.ready(), grabbing the element with jquery, and passing it into d3.select, but that didn't work either. Edit Once I got the jquery document.ready() syntax right, it worked.

Any way I can include the javascript at the top of the page and still select an element below? Thanks.

<script>$(function(){var svg = d3.select("#chart").append("svg:svg");});</script>
<div id="chart"></div>

In other words, it's not happening because you can't query against something that doesn't exist yet-- so just do it after the page loads (here via jquery).

Btw, its recommended that you place your JS files before the close of your body tag.

Not enough reputation to comment yet so I'll just put this here:

To expand on Micah's answer - the browser runs your code top to bottom, so if you write:

<div id="chart"></div>
<script>var svg = d3.select("#chart").append("svg:svg");</script>

The browser will create a div with id "chart", and then run your script, which will try to find that div, and, hurray, success.

Otherwise if you write:

<script>var svg = d3.select("#chart").append("svg:svg");</script>
<div id="chart"></div>

The browser runs your script, and tries to find a div with id chart, but it hasn't been created yet so it fails.

THEN the browser creates a div with id "chart".

Use jQuery $(document) function...

$(document).ready(function(){

var margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var x0 = d3.scale.ordinal()
    .rangeRoundBands([0, width], .1);

var x1 = d3.scale.ordinal();

var y = d3.scale.linear()
    .range([height, 0]);

var color = d3.scale.ordinal()
    .range(["#98abc5", "#8a89a6", "#7b6888", "#6b486b", "#a05d56", "#d0743c", "#ff8c00"]);

var xAxis = d3.svg.axis()
    .scale(x0)
    .orient("bottom");

var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left")
    .tickFormat(d3.format(".2s"));

//d3.select('#chart svg')
//d3.select("body").append("svg")


    //var svg = d3.select("#chart").append("svg:svg");

    var svg = d3.select("#BarChart").append("svg:svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
    .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

    var updateData = function(getData){

    d3.selectAll('svg > g > *').remove();

    d3.csv(getData, function(error, data) {
      if (error) throw error;

      var ageNames = d3.keys(data[0]).filter(function(key) { return key !== "State"; });

      data.forEach(function(d) {
        d.ages = ageNames.map(function(name) { return {name: name, value: +d[name]}; });
      });

      x0.domain(data.map(function(d) { return d.State; }));
      x1.domain(ageNames).rangeRoundBands([0, x0.rangeBand()]);
      y.domain([0, d3.max(data, function(d) { return d3.max(d.ages, function(d) { return d.value; }); })]);

      svg.append("g")
          .attr("class", "x axis")
          .attr("transform", "translate(0," + height + ")")
          .call(xAxis);

      svg.append("g")
          .attr("class", "y axis")
          .call(yAxis)
        .append("text")
          .attr("transform", "rotate(-90)")
          .attr("y", 6)
          .attr("dy", ".71em")
          .style("text-anchor", "end")
          .text("Population");

      var state = svg.selectAll(".state")
          .data(data)
        .enter().append("g")
          .attr("class", "state")
          .attr("transform", function(d) { return "translate(" + x0(d.State) + ",0)"; });

      state.selectAll("rect")
          .data(function(d) { return d.ages; })
        .enter().append("rect")
          .attr("width", x1.rangeBand())
          .attr("x", function(d) { return x1(d.name); })
          .attr("y", function(d) { return y(d.value); })
          .attr("height", function(d) { return height - y(d.value); })
          .style("fill", function(d) { return color(d.name); });

      var legend = svg.selectAll(".legend")
          .data(ageNames.slice().reverse())
        .enter().append("g")
          .attr("class", "legend")
          .attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });

      legend.append("rect")
          .attr("x", width - 18)
          .attr("width", 18)
          .attr("height", 18)
          .style("fill", color);

      legend.append("text")
          .attr("x", width - 24)
          .attr("y", 9)
          .attr("dy", ".35em")
          .style("text-anchor", "end")
          .text(function(d) { return d; });

    });

}

updateData('data1.csv');

});