USERS can use the highcharts plugin

VAR chart=$("#container").highcharts();
Highcharts 2.3.4

Read from the Highcharts.charts array, for version 2.3.4 and later, the INDEX of the chart can be found from the data on the DIV

 var index=$("#container").data('highchartsChart');
 var chart=Highcharts.charts[index];
All versions
Track charts in a global objec/map by container id
var window.charts={}; 
function foo(){
new Highcharts.Chart({...},function(chart){
window.charts[chart.options.chart.renderTo] = chart;
});
}
function BAR(){
var chart=window.charts["containerId"];
}

Users can use the highcharts plugin

var chart=$("#container").highcharts();
Highcharts 2.3.4

Read from the Highcharts.charts array, for version 2.3.4 and later, the index of the chart can be found from the data on the div

 var index=$("#container").data('highchartsChart');
 var chart=Highcharts.charts[index];
All versions
Track charts in a global objec/map by container id
var window.charts={}; 
function foo(){
new Highcharts.Chart({...},function(chart){
window.charts[chart.options.chart.renderTo] = chart;
});
}
function bar(){
var chart=window.charts["containerId"];
}